To crease up is to laugh helplessly, or to make somebody do so. Crease up at the story.
The picture is of somebody folded double, which is what the crease refers to. It works both ways round, so a comedian can crease up an audience.
1phrasecrease upTo laugh helplessly, or to make somebody do so.
“The whole room would crease up whenever he did the voice.”
crease up is a phrase.
Practised in Phrasal Verbs