"
To lesbian" refers to a woman performing a task successfully with the required skill after a man says he doubts she is capable of doing it. Possible doubts
the silly man could have include something being too difficult for a woman to do or too complex for a woman to understand or to too heavy for a woman to lift.
It can also refer to anyone considered an underdog or lacking the required ability to perform a given task but who then successfully completes it.
The silly doubting man does not have to be present at the successful completion, or even show embarrassment at being proved wrong. What matters is that the capable woman completing the task knows she proved him wrong and feels proud she showed him who's boss.