I'm a female, and I think it's generally less easy for females to come standing? Or maybe not. Maybe at least less comfortable. I'm seeing talk of wobbly-legs.
I don't think I can get the sort of stimulation I need while standing up to come during intercourse. Oral stimulation might be hard for me, too, as it generally takes a lot of work for me to finish with that in any position.
My male significant other can come standing up--but seems to prefer the bed. He has always has had trouble in the shower because the area heats up too much during play? We hate feeling really hot while playing.
I think difficulties in some positions come because it's not what we're used to. If I'm not in my favored position, it's distracting when my aim is to come.