If I saw the scene the same thought might have popped into my mind as well. I mean a mechanic, how much more cliche can it get than that? Wait a lumberjack perhaps, but well nevermind.
However from the reaction of your mother I can tell she's of the conservative sort so it certainly won't be easy to convince her otherwise unless she actually caught you in the act with a woman. There's the plan I guess

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Just to join in on the other discussion: There's nothing wrong with being gay, as there is nothing wrong with being bi or hetero. What one does with his life should be his decision alone. The reluctance of some people to accept others for what they are is just a natural instinct: the fear of the unknown. This is as human a feature as our curiosity. The difference is which outweighs the other.