Yeesh, that's going way back..............
........ um... it's a hard call. It was either:
A: Josh Lesnic's Girly: A webcomic that came around in the chaotic early era of Webcomics. I think it's considered a pioneer of webcomics by the folks who actually care about that sort of thing. In hindsight it was kind of non-incredible. The art was really well-done in the later arcs but in this day-and-age that's kind of, well, join the club you know? But I was less discerning as a kid.
or
B Smorky's Purple Pussy: A webcomic that doesn't have anywhere near as much sexuality as your probably thinking but still managed to be far more adult then the time period it came out in thought was appropriate. Touted as a, "webcomic for girls", it was more of a hardcore LBGT webcomic when that was still in the dark-ages of acceptance.