When Lisa and Beth try to convince Mr. James that the fight is a bad idea, Lisa mentions that the fight will take place in a boxing ring. Mr. James promptly corrects her, saying it will take place in an octagon, or as he calls it, an "octagon of horror". However, when the fight actually takes place, it is in a normal boxing ring.
Although there is no criminal code that has to deal with 420 or its relation to marijuana, there was a California Senate Bill numbered 420 that dealt with medical marijuana. This bill passed September 11, 2003.
Dave: (about Bill's tape-recorded phone call with Lisa) Bill, please tell me you're not the kind of person who would go down to the loading dock tonight and rummage through the trash to find that tape.
Bill: How do you think I got Lisa's home number in the first place?
Lisa: What about that sweet 18-year-old kid in accounting who had that crush on you?
Dave: Oh, that was completely different.
Dave: Well, for one thing, he was a guy. And he was convinced that I was gay. And he brought his mother to work and introduced me as his boss-slash-husband.
Lisa: Well, it was still flattering, wasn't it?
Dave: Oh, Lord yes.
Dave: Bill, you didn't tape-record a phone conversation with Lisa?
Bill: Oh, relax, Dave, she didn't KNOW I was taping the call, she had no idea!
Bill: Are you challenging my constitutional right to make nude phone calls?
Matthew: You're going down, bitch.
Dave: Don't forget, everybody. We're all invited to Mr. James' smoker this evening.
Beth: What is a smoker, anyway?
Walt: Oh we used to have those in college all the time, where you turn the lights down, crank up a little bit of Dark Side of the Moon...
Dave: No, Walt. This is a different kind of smoker.
Joe: (before the fight) Whatever happens, I just want to say I love ya.
Andy: That's sweet, but no sex before the fight, okay?
Walt: We used to have those in college all the time, where you turn the lights down crank up a little Dark Side of the Moon..."
Dark Side of the Moon is an album by Pink Floyd, that tends to be a fan-favorite.
Although this episode is numbered as Season 4, Episode 20, the title "4:20" actually is a reference to an urban legend about smoking marijuana at that specific time of day.