Screw up Definition 1 of 3Pro Tip 1/3Informal Usage Used more in casual conversation than in formal writing or speech. I screwed up by telling the joke at the meeting. Pro Tip 2/3Responsibility Expresses personal responsibility for a mistake. I need to apologize; I really screwed up. Pro Tip 3/3Regret Potential Often used when there's regret or remorse over the action. He screwed up and felt terrible about it for days.