BRITNEY SPEARS' EX I Need Hotter Hair TO BANG CHICKS

Britney Spears' newly-single ex-fiance Jason Trawick is on a mission to get laid ... but he couldn't perform without a buzz.

Trawick's stylist Nik Rae Falco at TRIM in Venice tells TMZ ... Jason's been bummed ever since his engagement with Britney fell apart in January ... so last week, she offered to give him a fresh new haircut to "sex him up a bit."

Nik says Jason replied enthusiastically, telling her he wanted to look good in order to meet girls -- so he gave her free reign.

Jason showed up Friday to get his new 'do ... and Nik gave him the "forget the girl" special -- shaved sides, longer on the top. Kinda David Beckham-y.