pinch (one) off
vulgar slang To defecate, especially quickly. Give me a minute, I just need to go pinch one off and then I'll be ready to leave.
pinch something off (of) something
and pinch something offto sever something from something by pinching. (Of is usually retained before pronouns.) Pinch the buds off the lower branches so the one at the top will bloom. Pinch off the lower buds.