Member here, not model, so I'm limited in my knowledge on this, but what comes to mind initially:
1.) If these are gifs or pictures that are hosted on CB (e.g. typing ':' and then <text> for a gif), I'd think about contacting CB support to see if those can be removed. To my knowledge, I believe gifs/pics are supposedly scanned before posting, but it's always possible some got through.
2.) I imagine this is probably a grey user, right? If so, I'd consider blocking grey users and keeping the chat to members w/ tokens only. (This would also significantly reduce all spam bots too). If it isn't a grey user, I'd contact CB support to see if they can do something like block his payment options so he'll stop signing up for non-grey accounts.
Also, I sincerely doubt you'd get in trouble for this, considering you are not engaging in the behavior at all.