a person that everyone laughs at because they have done something stupid
a laughing stock
to secretly think that something is funny
to laugh up one's sleeve
to say funny things with a serious, calm expression
to have a dry sense of humour
to not smile or laugh
to keep a straight face
to find something extremely funny
to roll on the floor laughing/to die laughing
to play a joke on somebody, usually by making them believe something that is not true
to pull somebody's leg
looking very happy, especially soon after you have been looking worried or sad
to be all smiles
