Matt Damon Bombed with Bird Poop While Hanging with Chris Hemsworth

Matt Damon made the mistake of sitting next to Chris Hemsworth in public, and Mother Nature made him pay for it -- well, a large bird with full bowels actually made him pay.

Check out Matt's shirt -- front and back -- 'cause he got bombed by some bird down in Byron Bay, Australia. Matt spent Sunday hanging with Chris and his fam at the beach -- y'know they're locals in the Bay.

Matt seemed slightly amused after the s**tstorm, and attempted to clean up. He also changed his hat ... just in case.

Far as we can tell, Thor emerged totally unscathed, still ridiculously hot ... and without sleeves.