Ah, an interesting point being discussed here. Most times, the MEL covers it. When something clearly is not working at all it is easy! However, you can have situations where a system is not operating as "advertised" but some pilots are happy with it during the inevitable "have you flown x-abcd recently? have you noticed..." type issues. In many cases "inferior piloting skills" are implied so you tend to shut up as everyone else is coping. How do you deal with that?