When you or someone else puts out a cigarette, blunt, joint, etc. somewhere on your body

Tattoo of Greek letters, crest, or other Fraternity symbol on ones body.

You get a frat tat when you take a cigarette and burns yourself with it.

A Frat Tat is when you put roofies and a young lady's drink, have sex with her and before she awakens from her roofie induced slumber, draw all over her face with a magic marker.