Chad Johnson Lights Up Cigar During College Lecture

Chad Johnson was straight fire during a lecture at the University of Florida Thursday morning -- blazing up a cigar in the middle of class ... despite the fact it's a non-smoking campus!!

The ex-NFL star was the guest speaker at a sports media class on the UF campus -- and cracked jokes about all sorts of stuff ... including his ever-changing last name.

But Chad got the most laughs when he pulled out his stogie -- and actually began to smoke it during the class!!!

FYI, UF has touted itself as a tobacco-free campus since 2010 ... but if you think a little rule is gonna stop Ochocinco ... child, please.