There is a feminist YouTuber who I'm a big fan of called " Liana Kerzner" (her channel is "Liana K"), and a while back she made some really good points about how the term "incel" should not be used as it is derogatory. Here are some of her quotes:

https://twitter.com/redlianak/status/1230143696542355457

No feminist should be using "incel" as an insult. It's rooted in the toxic idea that men are only "real" men if they have sex. How much sex you have or don't have does not determine your worth. Stop attacking people based on the idea that it does.

https://twitter.com/redlianak/status/1117195466452688897

Observation: people call men "incels" the way they call women "sluts" as a pejorative. This is all sexist because it ties "acceptable" sexual activity to gender in an unequal way.

https://twitter.com/redlianak/status/1161327001489281024

It's so odd seeing the left adopt "incel" as an insult. Attacking a man for a lack of sexual activity used to be considered somewhat bad but its totally ok nowdays.

https://twitter.com/redlianak/status/1294992760324358144

A reminder that when you use the term "incel" as an insult, you're tying a man's worth to his sexual activity. Which Makes men do extreme stuff to get sex. It's amazing how many people don't stop using that insult when that's pointed out.

After reading this, I was actually convinced to try and make this point every time I saw someone using the term "incel". The result? Downvoted to oblivion while the OP comes out and brags about how they're never going to stop using the term even though they know it hurts people. It never really occured to me before I saw Liana K point this out, but it's actually quite unsettling when you think about it how this has level of shaming and hatred has been normalised.