During an argument with some people, I come to the conclusion that they are either stupid, ignorant or liars.
Let's imagine that we have 2 guys discussing what color they should be painting a room. Person 1 clearly wants his way (paint it black), and refuses any and all arguments from Person 2. Person 2 attempts to reason with Person 1, and provides several good reasons not to paint it black. Person 1 responds with insults.
Person 1 clearly appears to be insensible and illogical. This can be due to being ignorant (not understanding the premise/vocabulary), it can be due to being a liar (pretending to be ignorant), or alternatively it can be due to being stupid.
Assuming Person 1 is being honest in this situation, and understands the language completely, it's relatively safe to assume that he's stupid. The problem is the following:
After concluding someone is stupid, via logic, when is it ethical/correct/not a fallacy to point out that that person is, in fact, stupid?
Furthermore, is it acceptable to attempt to continue trying to provide arguments against such people?