Excessive knotting of a clump of hair at the back of ones head caused by frenzied rubbing back and forth of said clump during sex, the physical act of love, coitus...
Limecat: Dudette, you got a mean motherfucking shag tat, what's went owwwn...
Clockspider: Manbitch and me, we had sex aaaall night honey. No time to brush my hair, all shagged out. get me?
result of a good night between the sheets
Boss: Your hair is a mess. Sort it out employee
Employee: Shut up and get yourself a good shag tat, bitch.