Tila Tequila's GF Gets Slap Happy in Vegas

TMZ has learned Tila Tequila's lesbian girlfriend was arrested in Vegas last night -- for allegedly hitting on a guy!

According to law enforcement sources in Las Vegas, it all went down outside of Pure nightclub when a boozed up Courtenay Semel, daughter of former Yahoo! CEO Terry Semel, "smacked" a security guard in the back of the head on her way out of the place.

Courtenay was immediately detained by Caesars Palace security while members of her posse -- including Vegas showman Jeff Beacher -- waited for cops to arrive. Four hours later, law enforcement arrived and issued Semel a citation for battery. We're thinking daddy can probably cover the fine.

Attempts to reach a rep for Semel were unsuccessful.