Peter, it's a cultural thing: North Americans behave differently from central Europeans in this respect. Effectively it boils down to perception of "politeness." Responses you may perceive as impolite may be perceived by others as entirely appropriate, and vice versa. IMHO the appropriate response on both sides of the Atlantic is to ignore any perceived petty insults to focus relentlessly on substantive issues. People either respond in kind in which case you can have a useful discussion, or they don't. C'est la vie.