Gilbert Gottfried -- Channing Tatum's Penis Nickname Comes Up Short

Gilbert Gottfried is a real dick.

Gilbert was cruising past the TMZ NYC Tour bus Thursday when our photog asked about Channing Tatum's homage ... nicknaming his penis "Gilbert."

In case you missed it ... Channing revealed on a Reddit AMA his penile nickname is Gilbert.

But sadly for Channing, Gilbert says there's a big ... actually a small clue when guys name their junk after him.