1. vulgar slang To be very stiff, rigid, or inflexible in one's posture or demeanor. The guy trundled around the stage so gracelessly and awkwardly, as if he had a poker up his butt. You'd think she has a poker up her butt from the way she sits in class.

2. vulgar slang To be very rigid or inflexible in one's opinions or beliefs. My grandfather had a real poker up his butt when it came to people living together or having children before marriage.

3. vulgar slang To be irritable, unfriendly, or humorless. Geez, it was just a joke—you must have a poker up your butt or something. I wouldn't mess around with Mr. Daniels, he's got a poker up his butt today.