I think it would be good to separate the analysis into FGCA's which are always fallacious, versus those that are only warning signs/rude. For instance, the fallacy of grey is indeed a fallacy, so using it as a counter-argument is a wrong move regardless of its generality.

However, it may in fact be that your opponent is a very clever arguer or that the evidence they present you has been highly filtered. Conversationally, using these as a counter-argument is considered rude (and rightly so), and the temptation to use them is often a good internal warning sign; however you don't want to drop consideration of them from your mental calculus. For instance, perhaps you should be motivated after the conversation to investigate alternative evidence if you're suspicious that the evidence presented to you was highly filtered.