Jeff Dunham -- The Moment I Knew Bruce Jenner Was Becoming Caitlyn (TMZ LIVE)

Caitlyn Jenner's transition completely blindsided comedian Jeff Dunham -- one of her homies from her Bruce days -- and he's revealing how he finally got the picture.

Dunham was on TMZ Live Thursday ... responding to Caitlyn recently calling him out for avoiding her. Jeff says he doesn't have any issue with Bruce becoming Caitlyn. In fact, he says even though he noticed a few plastic surgeries over the years ... he NEVER suspected what was really happening.

But JD says he finally raised it with Jenner after one particular magazine cover. You gotta hear how the convo went down, and how Jenner broke the news.

As for reconnecting with Caitlyn -- Jeff says it's gonna happen soon, and it's a scheduling issue, and NOT about awkwardness.