President Obama Passes Drug Test from Tommy Chong ... Bill Clinton Does NOT

Bill Clinton definitely didn't inhale because it's likely he never even had a joint, according to Tommy Chong who says Bill failed a simple test ... which our current Prez aced.

The 'Cheech and Chong' star was at LAX signing autographs and fielding questions about all things weed ... when we asked which past commander in chief he'd invite for a smoke sesh.

Naturally, we were expecting Clinton's name would be mentioned -- based on his infamous I "didn't inhale" comment. But Tommy shocked us when he explained why he doesn't buy Clinton's marijuana confession.