Older Ted – "Back when we were dating, Robin and I had this running joke and we were the only two people that found it funny. And we did it all the time." There are different circumstances in which they laughed and did a salute at any mention of military men, like generals or corporals. "Because once you start, it is surprisingly hard to stop. But now, we were broken up, so now when Marshall said '…major pay raise,' we just let it slide. You see, on the surface, Robin and I looked like we were doing great, but the truth is that trying to be friends with your ex is a lot harder than it looks. You can't be as candid as you used to be, but most importantly, you can never, ever be alone together."
Lily shows up with the turkey at the bar and they are excited about Thanksgiving. Robin tells them that she is going to bring Bob, her new boyfriend, since he didn't have anywhere else to go. Lily freaks out since it is their first Thanksgiving together. Robin apologizes and tells them that the real Thanksgiving is the Canadian Thanksgiving. Barney takes offense to that and asks what Canadian have to be thankful for. Robin explains that it is to celebrate Martin Frobisher's attempt to find the Northwest Passage. Marshall invites everyone over to watch the Slapsgiving Day Parade, to which Barney points out that he said "Slapsgiving" again. Marshall explains that Slapsgiving is a new holiday that he has come up with and they give each other slaps. Older Ted – "I should explain. Kids, you remember the slap bet. A year earlier, Marshall made a bet with Barney and won the right to slap him five times. He had already used the first, and the second, but Marshall had something special in store for the third. Marshall reminds Barney about slapcountdown.com that appeared in another episode. Barney tells Marshall that the countdown ends at 3 pm on the day after Thanksgiving. Marshall apparently counted the days wrong and it turns out that Slapsgiving is on Thanksgiving. Lily is the slap bet commissioner and allows the slap. Barney tells Marshall that he is not scared since he now knows when the slap will happen. Bob shows up and Robin gets up to meet him and tells them that he is 41. Older Ted – "Ok, kids, the truth is that Bob probably looked like this, but when your ex is dating someone new, you always have to accentuate their flaws. This is how I saw Bob." Ted sees Bob as a 60-year old man who talks like a teenager when he tells them that he had to talk to his parents. They walk off and Ted thinks that he looks like Orville Redenbacher. Lily tells them that they are making pies at Robin's house since Marshall likes to sleep eat. Ted shows up at Robin's apartment and learns that everyone else is doing something else. They are both nervous about being alone together. Ted calls Barney and asks him to come over, but Barney is hitting on a girl. Older Ted – "After a very long night, it was finally the big holiday, sorry, the two big holidays. Lily is running around getting things ready and Marshall reminds Barney about his impending slap. Ted opens the door and Robin walks in with the pies. Both Ted and Robin talk to Marshall and Lily separate.
Ted tells Marshall that being together while making the pies was awkward and they didn't know what to talk about. Barney tells Ted that you don't want to hurt her during a holiday and talks about not wanting to hurt anyone during a holiday. Marshall tells Barney that he is still getting slapped. Ted continues his story and Robin talks to Lily about wanting Ted to leave. Lily wants Robin to help her get ready, but Robin tells Lily a story about what happened while they were making pies. Ted brings up having sex lots of times during last Thanksgiving and Robin didn't know what to say in response. Robin makes a pecan pie and when Ted reminds her that she is allergic to pecans, he figures out that Robin is making the pie for Bob. Barney and Marshall are shocked that Robin had her making pies for Bob. Ted and Robin talk about Ted being jealous about Bob, but Ted tells her that he is jealous of Bob because he is so old. Robin gets upset and they start arguing about how they feel about their new significant others. Ted decides to leave, but they begin kissing.
Marshall, Barney, and Lily are all shocked that they slept together. Lily reminds Robin that she is sleeping with another man while she brings another guy to Thanksgiving. Lily asks if they talked about it and they did not. They both decide that they need to talk about last night. Robin and Ted start arguing about who started what they did the previous night. Lily breaks up the fight and puts them into Ted's room to figure everything out. Marshall puts the computer with the countdown on the table to remind Barney about the slap that will happen in a little over 2 hours. Marshall tells him that he will slap him so hard that he will go back into time. Barney starts crying and tells Marshall that he is so nervous about when he knows that the slap is happening. Barney is about to leave, but Lily tells them to stop thinking about themselves and as the slap bet commissioner, she tells them that Thanksgiving will be slap-free. Bob shows up with jell-o shots. Ted and Robin are in his room talking about how they are going to try to be friends, but Ted realizes that they can't be friends. Robin suggests that they should stop pretending. They decide to eat dinner and then stop being friends. Robin walks out of the room, leaving Ted alone. Older Ted – "So, we sat down to our first Thanksgiving together as a group and apparently our last." Marshall asks if Lily would like to say a few words, but she wants to eat. Marshall decides to do the toast and thanks Lily for making a new tradition. Bob starts talking about how his Thanksgiving at his parents' house is crazy and Older Ted says "…then a funny thing happened…" and when Bob says "…major buzz-kill", both Ted and robin salute at it. Older Ted – "You see kids, friendship is an involuntary reflex. It just happens, you can't help it. That first Thanksgiving turned out to be a wonderful dinner with the four people I loved most in the world and Bob. And it did become a tradition. That's why, every year, we go to Aunt Lily and Uncle Marshall's for Thanksgiving." Barney tells everyone that they are twenty seconds until the slap countdown is over. While Barney is talking smack to Marshall, the computer starts talking and it counts down from 10 to 1. Lily wants Barney to put it up and then gives Marshall the permission to slap Barney. Marshall slaps Barney and then runs to play the song that he has composed for this special occasion. Ted turns off the lights and starts playing a song about slapping Barney.
During the clean-up, everyone salutes when Ted says "major cleanup" and then when Robin says "general idea".