Truthfully, I can't tell how upset Biden actually was, and he may have been kidding. But I think Biden's words are telling:
"Why don't you say something nice instead of being a smartass all the time."
All the time???? How often do you suppose Biden converses with this manager of a Kopps Frozen Custard place in Milwaukee? This manager seemed to represent all critics to Biden; why can't you just be nice, why do you have to actually remind me of the policies I support. Biden, who was in Milwaukee campaigning for Senator Russ Feingold said he was just kidding with the manager. Maybe. But it could also be the quick-witted manager struck a blow that landed too close to the truth for Biden.
Perhaps he should blame a brain freeze. People would believe that of Biden whether he was noshing on frozen custard or not.