Something common in incel spaces (and those who frequent them) are people with very low self-esteem. They often have little to no internal compass. They feel lost, they don’t know where they’re going. Maybe at some point they’ll annoy you, because their complete nihilism causes them to act strange.
At this point you might insult this incel, or incel-sympathetic person. This is where the low-self esteem person finds a path, a way to feel balanced. They internalize the insult and just runs with it. Not just the mere word attached to the insult, they’ll interalize the core of what that word means. They’ll watch Youtube videos about their new identity, talk to their friends about their new path and build their life around it (for at least a few months until someone knocks them on a new path)
The exact same thing happens with compliments.
Apart of this is related to being socially isolated, where one can just pick a path or ideology out of a hat and not feel social consequences for doing so. Insult or compliment an incel as a Nazi and they’ll probably just run with it. Compliment or insult an incel as a peacenik hippie and they’ll also probably run with it.