Perhaps you need a bit of space right now? Setting some boundaries for yourself is ok. You can still do that and continue to feed. It's one of the best things about continuing to feed through toddlerdom (and little appreciated since most mothers who feed in our society do not do so for long).
If you'd like him to ask nicely, then tell him so. It's not unreasonable - you probably don't offer him other foods or cuddles if he yells or accosts you in that sort of way, right? You can do this with love and understanding and it helps him to learn to interact with others with greater sensitivity.
My daughter got into the habit of pinching when she wanted milk. She's now signing milk and please. Much nicer. Unless she's really frantic, then she still pokes me sometimes, but that's not so bad as pinching.
Also, you're allowed to be flexible and change the rules as conditions change. that's ok. it's really up to you and what feels right at any given time.