to have sex or get really comfortable with another person... usually of the opposite sex...
Koby wasn't just shackin it up with monika but with every other girl out there except for me cuz i dumped him!!!!
by Koby's ex... same one as above June 26, 2003
to get it goin on with another person... having sex...getting close and cuddly with each other
Monika and Koby was "shackin it up" with each other in the bed
by Koby's ex June 26, 2003