This has never happened to me, being pushed aside by manspreading. I don’t ride a lot of public transport (what’s that? Lol) so maybe that is why. I have seen another kind of “manspreading” which is when guys wear athletic shorts without underwear and sit like that, and unintentionally share some views of what should not be seen in public.
In most cases they probably aren’t doing it deliberately. They’re just too dense to realize it, or too generally inconsiderate a person to even give it a thought.