If someone tells you a word is offensive (regardless if it's bannable or not) maybe you shouldn't say that word. The r word is very hurtful for folks who are disabled and neurodivergent. As we are in a public forum, let's do our best to make sure everyone has a space where they feel wanted/welcomed.
Both the r word and dumb are offensive, as dumb is a perforation used to mock the deaf and hard of hearing. Pretty much most euphemisms for peoples intelligence have some offensive a list roots. Society has come a long way.
