Just my 2 cents here ...seen the website, while I do not really agree with the intent, that's not why I am commenting.
A number of people have highlighted the possibility of defamation lawsuits, I think the founder needs to definitely ensure they have robust Ts & Cs and Disclaimers to cover their backs.
I however think that the chances of any defamation lawsuit actually succeeding is very very low. The platform as set up does not show enough specificity to meet one of the criteria for a successful defamation suit i.e. it must refer to the claimant.
Even if the person posting the information then goes on to mention information that can narrow it down to a specific person and meet the criteria for referring to the claimant e.g. Femi from Ibadan who is the manager at Amala Unlimited is scum because he did blablabla... this might not necessarily mean a defamation case will still succeed. If the lady alleging the 'scumminess' of the individual is actually stating the truth, then truth is an ultimate defence to a defamation suit.
All menarescum.xyz would have to do is ask the poster to do before posting a 'scum receipt' would be to click an indemnification type clause that the info they are posting is true, and that they will indemnify the website if there is a lawsuit...not watertight, but could work.
Anyway, this is NOT legal advice, speak to a lawyer for more detailed information/advice.