For the exact same reason they want to talk if you make the mistake and use a bathroom without stall doors, no real respect for personal privacy.

Or if you want to think of picking up a lady as hunting, then they are the scavengers ready to swoop on whatever you leave behind.

I do know what you mean, I just tried to answer your question. Most of your replies to the forums seem to go off the topic or answer required. I think you even said this yourself.
That said, to step on someones toes means "You are creating problems" it probably came from idiology or such, during WW2. You could be rocking the boat as they say, without knowing it. There are many writing styles and interpretations of what we write, I say to my students to take it in context, don't read something into it, because that will, or could cause a problem.
I can't actually see where you have used the term in the question at all?

Chinese guys are notorious c**k blocks when it comes to women.

When I seen the topic I thought you meant it literally, which is also very true. It ain't a bus journey until someone has stood on your (clean white) shoes.

I tell them to phuck off quite directly in both languages