a rusty shotgun is when a female is eating out a mans asshole and proceeds to reach between his legs with one hand and begin jerking him off in a cocking motion as if cocking a shotgun; and using the other free hand to caress the man's testicles
We all found out Michael was gay when we walked in on him with his head in Fro's ass, giving him a rusty shotgun.
When a someone is giving you a hearty rim job whilst reaching around and fondling your balls like a gun handle and pulling your penis shaft with the other hand just like cocking a pump action shotgun .. This action is a variant of the rusty trombone
Sally gave me a rusty shotgun the other night and it felt great