Continuity mistake: When Robin leaves to get Battleship, Barney thinks they're going to have sex, whips his belt off, and throws it on the floor. When Robin returns, he's neatly folding his pants and draping them over a chair, and his belt is still threaded through the loops. (00:16:20)
Suggested correction: He could have easily done that himself so it was easier to put back on afterwards.
This correction is too much of a stretch. It would make no sense for him to take off the belt and throw it to the ground in the first place. He was alone at that point, so he wasn't doing it to impress anyone and he's been in this position before.
The Wedding - S1-E12
Continuity mistake: In this episode, Lily is in Robin's house with her dogs. In the episode "World's Greatest Couple", Robin reveals that Lily can not stay at her apartment because Lily is allergic to dogs.
Suggested correction: Doesn't mean Lily can't go over and visit for a while. My mother is allergic to cats. She can visit her cat-owning friends for a while, though she would never stay overnight. Pet allergies can be pretty controllable, as long as you're not constantly in contact with the animal.
Other mistake: At the beginning of the series, Ted starts telling the story of how he met the mother of their children. When he starts describing how he met Robin, he doesn't reveal that it was not their mother until the end of the pilot. But children should have realised it wasn't their mother when Robin said she was a journalist and worked as a TV presenter. The kids knew their mom wasn't a journalist, so they shouldn't have been surprised at the end of the episode when Ted said "this is how I met your aunt Robin".
