To think it’s weird to sit at someone’s table without asking?

[orancing]

I’m sat having a coffee waiting for my train and some woman has just plonked herself on the other seat … and not said anything.

I mean if she’d asked u would have said “of course” … I mean for all she knows I’m with someone.

Railway station is different to cafe: if there’s a seat free, I’m having it and I’m not messing about.

OP. Have you considered that you might be the weird one here?

It's not weird but it is at least presumptuous and verging on ill-mannered. A simple request to sit down is all that's needed.