There are two definitions:
1. v. Getting the ugly fat friend drunk off her ass so she won't cock block any potential hook-ups with her hot friends. This is usually with the intent that she'll lose her inhibitions and suddenly feel the urge to "just dance" while leaving her friends alone.
Sometimes the skinny friends instigate this themselves so it won't hurt their game or their friend's feelings.
2. v. getting so drunk that you're willing to have sex with a large rotundous woman.
1. Jason: That fat bitch keeps trying to talk to me and ruining my game.
Adam: Let's get some juice in that ham so she'll leave us alone.
Anne: God, Judith is running all the hot guys off. Let's buy some shots.
Jessica: For real, bitch gets crazy on the dance floor. I just hope she keeps her clothes on this time.
Becca: God that was gross but worth it. Fuck it - let's juice that ham!
2. God damn I was so drunk last night that I put my baby juice in that ham.
I'm so drunk and desperate I'll even go for juicing a ham.