Zach Galifianakis -- Is That a Black Eye?!

Zach Galifianakis ... who hurt you?

The "Hangover" star rolled up to Comic-Con in San Diego this weekend sporting what appears to be a bruise on his right eye.

We called Zach's rep multiple times to find out why the funnyman is sporting a shiner ... but so far, it's radio silence.

Zach was at Comic-Con to promote his upcoming political comedy, "The Campaign" which co-stars Will Ferrell.

Zach and Will sat on a panel together at Comic-Con Saturday ... but never mentioned his eye ... probably because nobody asked.