His behaviour is a dominance display, and IMHO has sexual dominance overtones. He sounds like a neanderthal. I doubt a verbal approach would work, as speech didn't evolve till much later in the evolutionary process. Find a non-verbal counter - here's one idea:

Have a largish, light object handy, a broad-rimmed hat would be ideal. As soon as he does the crotch display, pick the hat up and place it over his crotch while saying "I prefer not having to look at your crotch in such detail". Keep a neutral expression.

This will demean him, as it's almost a non-verbal emasculation and he won't like it, but being the neanderthal that he is, he won't show he doesn't like it.

If he removes it, put it back. If he repeats the behaviour in a later visit, just keep doing it.

If he closes his crotch by placing the crossing his feet on your desk, say "And by the way I don't like you putting your dirty feet on my desk".

Take charge of your space. Don't be threatening - alpha males don't like that. But don't be submissive, which is what you are right now - by not reacting, you're non-verbally saying "I accept you dominating/demeaning me in this way", which is reinforcing his sense of power. Let him know that in your space, you're in charge. Remove the power rush he gets and pretty soon he'll stop the behaviour.

He won't complain to HR (or anyone else) about you - even he must know at some level that his behaviour is appalling and he won't want to describe the situation to anyone.

His behaviour is a dominance display, and IMHO has sexual dominance overtones. He sounds uncouth. I doubt a verbal approach would work as effectively as a non-verbal one to a non-verbal behaviour, so dind a non-verbal counter - here's one idea:

Have a largish, light object handy, a broad-rimmed hat would be ideal. As soon as he does the crotch display, pick the hat up and place it over his crotch while saying "I prefer not having to look at your crotch in such detail". Keep a neutral expression.

This will demean him, as it's almost a non-verbal emasculation and he won't like it, but being the neanderthal that he is, he won't show he doesn't like it.

If he removes it, put it back. If he repeats the behaviour in a later visit, just keep doing it.

If he closes his crotch by placing the crossing his feet on your desk, say "And by the way I don't like you putting your dirty feet on my desk".

Take charge of your space. Don't be threatening - alpha males don't like that. But don't be submissive, which is what you are right now - by not reacting, you're non-verbally saying "I accept you dominating/demeaning me in this way", which is reinforcing his sense of power. Let him know that in your space, you're in charge. Remove the power rush he gets and pretty soon he'll stop the behaviour.

He won't complain to HR (or anyone else) about you - even he must know at some level that his behaviour is appalling and he won't want to describe the situation to anyone.