Making out with someone
Can also be used in differnt contexts:
-Julia: "OMG I saw Brittany macking Christina's boyfriend!"
-Haley: "Ugh Julia is such a whore, she macks every guy she sees."
-Melissa: "Did you see Josh at that jam this weekend?"
Christy: "Ya we pretty much macked all night"
-Caitlind: "You better mack him he's fucking sexy"