Here are a few of my favourite moments :
When Monica and Ross perform ''The Routine''
When Rachel discovers that Ross hadn't finished reading her letter and she says '' You fell asleeep???!!'' The way she says that is hilarious!
When Amanda starts dancing in front of Chandler.
When Joey and Chandler go on a double date and Janice shows up.
When Phoebe tries to 'seduce' Chandler and she starts dancing, that's so funny!