'Baywatch' Star Sues Agent -- I Want My $100K Back!

Ex "Baywatch" star David Charvet -- who played buff lifeguard-man Matt Brody -- claims he got screwed over by the one guy who's supposed to have his back ... his agent ... and now the actor's out $100,000.

Charvet filed the lawsuit Monday in L.A. County Superior Court -- claiming he loaned his agent Tom Chasin the six figure sum last June for a period of six months ... but the December deadline came and went, and Charvet still hasn't seen a penny of it.

No word on what the loan was for, but Charvet wants payback asap -- demanding the $100,000 he loaned out, plus interest.

Calls to Chasin haven't been returned.