If they are roleplaying I'll just roleplay what my character would most likely do. Usually it would probably be my character wouldn't care and keep on doing, regardless of the size. XD
But if I were not roleplaying and neither was the person, then my reaction would probably be to stop what I'm doing that is bothering them. Again, size doesn't matter for me.
I guess it depends on the person, but I don't really think size makes a difference. In real life, if a huge muscular man tells me to do something and he's polite I'll respond by doing it, unless it's like a bad thing or something.
If a small little child tells me to do something in a really rude way, I'll find their parent or whoever is taking care of them and just leave them with the parent or the person taking care of them.
It just depends on how the person is talking to me and what previous experiences I have had with them.