People that whoop and cheer at jokes in a comedy show.
If its funny laugh, or at most clap if it’s clever. American comedy shows are full of people that just go ‘WOOOOOO’ after a joke, and it’s starting to come over here a bit too.
‘Woo’ is only an appropriate response if they state an agreeable opinion, or at the end of the show to give appreciation. Not after a random joke, that’s not a normal response.