Because you're annoyed (who wouldn't be at least a little bit) but you're being all nice about it. I know when my parents get annoyed at me, I prefer them to yell than be nice about it. When they act all accepting, I get a temporary feeling of off-the-hook-ness, but the guilt gets me later. ;_;
Actually, scratch that. I don't like being yelled at. You know what I mean, though, right?