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1.
v. to continue sexual relations with multiple partners simultaneously, a la Tiger Woods.
Man, Tiger was multi-assing all those bitches!
by Staypuft75 December 15, 2009
 
2.
To be doing more than one ass at once.
"dude last night i got so much ass at once"

"so you were multiassing?!"

"pretty much!"
by Falalala. January 02, 2010