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1.
A sexual act in which a person gives a blowjob while humming the U.S. national anthem.
Man: Give this soldier an "Uncle Sloppy Sam"!
Soldier: What the hell is that?
Man: It's where he gives you a handjob...with his mouth while humming the national anthem!
by TontoTheScalper May 03, 2011
 
2.
giving someone a hand job, with your mouth, whilst humming the national anthem
For the 4th of July i decided to give my boyfriend the ultimate patriot's gift, an Uncle Sloppy Sam
by TruGun May 26, 2011