—used as a euphemism for fuck in various senses of the word
You don't eff with[=mess with] the Tupac legacy. You just don't. Olivia Jade KhouryA guy who likes you a bit more than you like him generally … doesn't eff with your mind. Jessica KnollShe told them to eff off[=scram].… he sees this age of mass travel, mass entertainment and mass culture as the best of all possible ages. Anyone who disagrees, he snarls, had better eff off now. Robert CarverToronto city council huffed and puffed, the Ford brothers blustered and bullied, the mayor even admitted to buying drugs while in office, and there were renewed apologies: "There is nothing else to say, guys. I really effed up[=messed up]." — Toronto StarThey threatened to eff him up if he didn't cooperate.He says something at the end of the movie that effed me up[=upset or shocked me]. Teresa Jusino
—used as a euphemism for fuck—used especially with the as a meaningless intensive
told him to shut the eff up… the bug that flew directly into your eyeball … may have caused you to freak the eff out. Megan Falk"… Now they're bleeding firing at us! They've never done that before—what the eff's going on?" James ClavellWho the eff doesn't like fry bread? Julien Perry