Dillon Ups Chuck on His B-Day

"Entourage" star Kevin Dillon celebrated his birthday in Vegas this weekend -- with none other than his TV nemesis -- UFC superstar Chuck Liddell.

The pair met up at Body English at the Hard Rock Saturday night. Liddell cameoed in an episode last season, in which he portrayed himself. In the ep, Liddell had a beef with Johnny Drama -- but it was all part of a hidden camera show.

Hard to believe Matt's little bro is 42. Victory!