Board Thread:Support Requests - Community Management/@comment-30818187-20200202094843/@comment-38078079-20200202123156

Sure, but the ToU do state:

"You agree not to:
 * Abuse, harass, threaten or intimidate other Fandom users;
 * Post or transmit any content that is obscene, pornographic, abusive, offensive, profane, or otherwise violates any law or right of any third party, or content that contains homophobia, ethnic slurs, religious intolerance, or encourages criminal conduct;"

Due to "retard" being an ableist slur, I would say this counts as "abuse" and "offensive" content, and could at least warrant in the admin receiving a warning (albeit - for a potential first offence - it's possible Fandom might not ban the user). I'd agree with VanityFiend that it's worth sending in a a report, as it's unacceptable language and should be looked at by staff.