'CSI' -- Alleged Gay Bashing Boss -- My Best Friends are GAY!

A "CSI" honcho who's being sued for alleged outrageous homophobic antics -- including drawing penises on the workstation of a man he thought was gay -- now says it's BS, because some of his best friends are homosexuals.

A set painter -- who says he's straight -- claims his supervisor, Jeremiah Redclay, went on a 5-year campaign of terror, calling him a f***** and other choice words, and plastering his workstation with crude drawings of gay sex.

Now Redclay's lawyer tells TMZ ... "CSI" execs FIRED Redclay over the allegations, but Redclay denies he did anything homophobic.

The lawyer says Redclay is totally down with gays ... he even has a close family member who's a member of the tribe, adding his client believes sexual orientation is simply irrelevant.

The lawyer believes the set painter got laid off and created a bunch of phony allegations so he could get his job back. Fact is ... "CSI" hired the set painter back after the allegations surfaced.