Honestly I'd kick my friends' asses for doing that. But this is a moot point because my friends know I'm more than capable of standing up for myself, and if I don't, there's a reason for it. I practically had to physically restrain my wonderful future husband from going to my dentist's office after she tortured me (drilled on my root canal tooth without anaesthesia) because I didn't want him physically menacing someone who was still doing work on my mouth!
It depends on the situation. My rule of thumb is that I never bring up anything that happened during a job unless the party (deaf or hearing) brings it up first. 90% of the time you pick up your things and opinions and leave (and then vent to the one person you pick who gets to be your sounding board, who is not involved with the deaf community and will never know the people you're talking about). Never in a million years would I say something like "Man that hearing person is a moron" to a client afterwards...and if they say it, I will probably not agree whole-heartedly since I don't think it's professional. I don't have a problem agreeing that the encounter wasn't a positive one, though.
If something went really awry during the job, it is sometimes worth it to explain to one or both parties what happened so that they don't leave with a bad taste in their mouth that was caused by the interpreting. (If they simply don't like each other, that's not your problem.) If something goes wrong, ask yourself whether it would have happened if this was not an interpreted encounter. Also, is this a one-time situation that will not occur again, or an ongoing situation where all three parties need to be able to work together?
Interpreters, whether we like it or not, are sort of the accessible agent of the deaf community to hearing people, and as such we have a responsibility to make as good an impression as possible while still supporting both parties neutrally. Sound impossible? It often is.
