There is a common assumption that if you are being fucked in the ass you are a submissive and he is dominant.
Submission is the action of accepting of the will or authority of another person.
If a guy wants to get fucked in the ass, he is a bottom not a submissive.
If a guy doesn't want to get fucked in the ass by anyone, but lets a dominant individual do it, he is a submissive.
A guy who doesn't want to get fucked in the ass but lets everyone do it, is not a submissive. He is either a bottom masquerading as a submissive, very kinky, pathetic or has been *******/is high.