Zach Galifianakis lit up late-night TV, literally, when he decided to smoke some weed on HBO's 'Real Time with Bill Maher.'

Maher -- a longtime opponent of legislation outlawing marijuana -- welcomed Galifianakis (currently promoting his new buddy movie 'Due Date,' co-starring Robert Downey Jr.) to the set of his current-events talk show, where a live panel discussion ensued about California's upcoming vote on whether to decriminalize the drug.

"It's a tricky thing politically to jump on that bandwagon [and vote for the legalization of pot] because I think that maybe people still see it as taboo," said the 'Hangover' star.

Pulling a joint and lighter from his sportcoat, the funnyman proceeded to puff away -- pausing to allow conservative reporter and fellow guest Margaret Hoover to sniff his prop and confirm it was the real thing. Fire up this clip and see the outrageous moment for yourself: