1. To become creased or wrinkled, as of clothing. After sitting for so long in my suit, the pants are starting to crease up. Don't worry, if anybody's clothes creased up in transit, I have a steamer with me. I didn't realize this dress was crumpled up in the back of my closet for a year. It's so creased up that I don't know if it'll ever look right again!

2. To cause something to become creased or wrinkled. In this usage, a noun or pronoun can be used between "crease" and "up." Hey, watch it! You're going to crease up my dress if you sit on it like that! Mom, why do you bother ironing the sheets? You know I'm gonna crease them up in one night. Aw man, I creased up my paper pretty badly on the way to school. Do you think the teacher's gonna take points off?

3. To become seized with laughter. Primarily heard in UK. We all creased up as Bob told us his hilarious story about his misadventures in the Australian outback. Your sister is so hilarious—I always creased up when she's around. It's hard not to crease up around toddlers because they just say and do the most ridiculous things with total seriousness and conviction.

4. To cause someone to become seized with laughter. In this usage, a noun or pronoun can be used between "crease" and "up." Primarily heard in UK. The stand-up comedian had a few jokes that really creased up the audience. After this terrible week, I need a movie that will crease me up. I need to cry with laughter! Uncle Phil's dramatic retelling of his bizarre trip to the market creased us all up.