Usually the last or near the last words in a string just prior to an orgasmic climax.
Oh, yeah, baby, more, faster harder, yeah, oooh, I'm cumming, ahhhhhhhhhhh!
Possibly one of the most annoying/truthful lines in any porn or hentai. Shouted by anyone who is at their limit during sex, and is so overwhelmed by the intense pleasure that their minds literally backfire, forcing them to shout this due to a lack of words to properly describe what is about to happen.
Guy: Ah, FUCK, I'M CUMMING!!!!!!
Girl: Already? Man, you suck.
Guy: Yea, but your just as bad as me. in 3-2-1..
Girl: DAMMIT, IM CUMMING TOO!!!!