A more enthusiastic version of the word "fit" to describe a member of the opposite sex. Not only are they "fit" they are really "fit" thus rendering them "Phit!!!!!!"
You are watching a music video when Beyonce comes on in a gold bikini. You say to your mates, "Phit!" They will understand what you mean.
Originated on LS1.com, now on LS2.com, a member named MJSBossman punched a 12 year old boy at the movie theaters because he was being an annoying little prick, the term was coined by Bravo on LS1.com. Variations included PYITS, PMITS, PTITS etc