This was a very amazing episode, and I would even go as far as saying it is one of the tiop three ever, if not number one.
There was a lot of amazing humour within the episode. Firstly, the concept of Barney as a hippie was so funny, and I couldn't stop mysefl laughing when I saw that. How awesome was that?!
I also loved the 'most embarrassing stories' that each of the characters told, particulary Lily's and Marshall's story of Marshall without his pants in front of Kindergarten.
Overall, there was so much great humour in this episode, I think it is just plain awesome! Keep it up, How I Met Your Mother, as this is going great!