Fuck up Definition 1 of 4Pro Tip 1/3Colloquial Use The phrase is very informal and may be offensive. Avoid using it in professional or formal settings. I can't believe I fucked up the presentation. Pro Tip 2/3Severity of Mistake Often used for significant mistakes that have noticeable negative consequences. He fucked up by missing the deadline. Pro Tip 3/3Emotional Impact Expresses frustration, self-criticism, or regret over the error made. I really fucked up this time.