The implied meaning of eating crabs is to be bold, we have a saying that you are the 1st person who dares to eat crabs, that is, the 1st person who dares to try, because the crabs look like they don't know how to put their mouths on them, but the 1st person who eats them understands the deliciousness of the crabs, which means that we do what we do to be bold enough to try, and we may get unexpected results.
Eating crabs between men and women refers to the first step between men and women, that is, to confess. The colloquialism is simplified to "eat crabs" which means to dare to be the first in the world, and to have the courage that others don't have. The relationship between a man and a woman is mainly a romantic relationship. How to make a relationship clear requires a man and a woman to take the first step bravely. And the person who chooses to take the first step is the meaning of eating crabs.