one other guy said that he shouldnt be playing if he didnt know he had the nuts. And he should get a penalty so he will know for the future
the two opponents didnt know each other.
This happened a few weks ago at DTD on my table
I politely told the lady that she isnt allowed to just flat call, but that I realised she didnt play often and was just letting her know. She seemed funny about be telling her the rules, fortunately the dealer backed me up. I did point out that just 5 mniutes before her husband was also on the table and people might take exception if he was her opponent. Then she got it.
I think if its clear they are a noob - just let them know after the hand
personally i love it when people flat call my raises with the nuts

if its clear collusion then obv they should get a penalty. Common sense to rule here imo