'Nirvana' Guitarist Pat Smear -- HUGE DONG ... Wife Says

Rock legend Pat Smear -- who played guitar for Nirvana and the Foo Fighters -- has a huge penis ... this according to an expert on the matter, his wife.

Pat and his wife were leaving Craig's in Hollywood the other night when we started talking about things like rock stars and devil worshiping (the usual).

During the convo, Pat's friend Bill Carroll (radio guy) made a joke about Pat having a tiny instrument ... and that's when Mrs. Smear chimed in and gave us the 411 on Pat's ginormous pud.