It doesn't have to be a sandwich.
Harold & Kumar Escape from Guantanamo Bay.
This term was used when Big Bob (a guard in Guantanamo Bay) asked Harold & Kumar to get hungry real fast and eat his cockmeat sandwich with extra mayo.
A type of blowjob that involves two persons sucking another one's balls at the same time, thus sandwiching the penis, or the "meat". This term was created by an awesome movie called "Harold & Kumar 2: Escape from Guantanamo Bay"
Big Bob - So are ya'll ready for your Cock Meat Sandwich?
Harold - Uhh.....no?
Big Bob - Well ya'll better get down quick! 'Cause i gotta whole lotta sandwich for ya'll....(cock comes out).
Kumar - So are you a homosexual for making us suck your dick?
Big Bob - THERE'S NOTHING WRONG ABOUT GETTING YOUR DICK SUCKED! YOU'RE THE ONE THAT'S GAY FOR SUCKING MY DICK!!
big bob: well you better get hungry real quick cuz i got a lotta meat
Kumar: tell me before we do this, are all the guards on guantanamo bay gay?
big bob: fuck no, aint nothin gay about getting your dick sucked.
big bob: your the ones who are gay for sucking my dick.
Big bob: infact it creeps me out just being around you fags.