Blake Lively's Halloween Costume: Flight Attendant!

Gossip Girl couple Blake Lively and Penn Badgley celebrate the 'Halloween 2033: Adult Playground Event Series' at NYC hotspot 1Oak on Saturday (October 31).

Blake, 22, was dressed up as a sexy flight attendant and was seen posing with one of the club's owners, Scott Sartiano, who dressed up as Indiana Jones.

Penn arrived with Blake hand-in-hand and celebrated his 23rd birthday during the Halloween party (they arrived after midnight). In the VIP section of the club, Penn was given a birthday cake compliments of Svedka Vodka with girlfriend Blake cheering alongside him. When asked what he was dressed up as, Penn told JustJared.com, 'I don't know! I'm a half-assed someone. It was a really last minute costume.' (He wore an afro, an athletic headband and a fake handlebar mustache. His t-shirt also reads 'Rope a Dope.')

Happy birthday, Penn!!!

10+ pictures inside of Blake Lively and Penn Badgley's Halloween party…