See, my main criteria for asking would be whether or not the server would feel comfortable saying no. Because not everyone is or can, and often with good reason.
This, and also, for me, whether the request is reasonable. If someone invites you to dinner, asking for seconds of what you’ve been served is perfectly reasonable. Asking them to cook you something else because you don’t like what you’ve been served is not. As a host, I’d feel terrible if I found out after the fact that one of my guests didn’t get enough to eat because they were too shy to ask for more and I was too dense to infer that they were still hungry. But I’d find it rather presumtuous if someone asked me to heat up a can of soup because they didn’t like my cooking–even though I would probably offer if I caught on to why they weren’t eating.