(I'm) not gonna lie

slang Used to indicate one's honest opinion about something, especially when that opinion may be unpopular, unexpected, or unfavorable. ("Gonna" is a colloquial spelling of "going to.") Ugh, I've been so bored this whole break! I'm not gonna lie, I'm kinda ready for school to start again. A: "The third movie in the series just ruined the whole franchise for me." B: "Really? It's always been my favorite one, not gonna lie." A: "And that's why I think women shouldn't enter politics." B: "Dude, not gonna lie, that all makes you sound like a misogynistic jerk."