Nothing says success like having your catchphrase shouted at you by adoring fans no matter how profane or out of context it may be. ''I'm here in New York doing [Neil LaBute's play Fat Pig] and people are screaming, 'Hug it out, bitch!''' laughs Jeremy Piven, who portrays cutthroat Hollywood agent Ari Gold on HBO's comedy Entourage. ''People remembered a line I improvised a year ago. I dig it.'' Indeed, the show's Sex and the City-with-dudes setup (and slimy L.A. insider-ism) is most memorable when the focus is on Gold. Piven, who's played a number of ''acerbic types,'' from PCU's supersenior Droz Andrews to Grosse Pointe Blank's suburban shlub Paul Spericki, admits, ''I've never played a guy in a position of power like this.'' His TV credits include a supporting role on Ellen and the 1998 dramedy Cupid that was beloved by viewers, but lasted only five months. Even though he's now freestyling quips with guests like Sarah Silverman and outshining handsome, younger costars Adrian Grenier and Kevin Connolly, Piven, 39, still thinks like a grunt in the trenches. ''I've been around, so I've learned not to get my hopes up,''he says, recalling his first movie role, in which he was billed behind Corey Haim. ''When I was 19 and did Lucas, I thought, 'Goddamn, I'm going to blow up.' I'm not that guy anymore.''