I think this is an interesting sentence. I know it means “What has that got to do with you?”
No, it means what has it/he got to do with it/him?
But can it also mean:
“What connection do you have with yer man there?”.
No.
Can you say: “Cén bhaint atá aige leis?” for “What has it got to do with you?” and “What is your connection to him?”
As with the others, you’re mixing up “leis”(with him/it) with “leat” (with you)
“Níl aon mhaith le duine ar bith aige sin” – He thinks nobody is any good.
To be honest, I don’t 100% understand this sentence myself. I know it comes from ÓÂ Donaill, so I am confident it’s right, but it’s an expression I haven’t seen before. I can only assume that the prototype, so to speak, of the phrase is “maith a bheith ag duine le duine eile” (literally, for someone to ‘have good/ness’ with someone else) means to think highly of someone or to think they are any good. “Níl aon mhaith …. ag an duine sin” = “that (the function of “sin”) person doesn’t have”, “aon mhaith le duine ar bith” = any good (here, meaning good opinion, I assume) with/for any person. Using this formula, if you wanted to say “I don’t think anyone is any good”, you’d presumably say “Níl aon mhaith le duine ar bith agam”. “The man doesn’t think the movie is any good” (assuming the idiom works for this type of thing) would be “Níl aon mhaith leis an scannán ag an bhfear”.
But that’s partially speculation, like I say, because I’ve never heard that before. Someone will probably correct me if I’m wrong.
I can appreciate that aige here mean “according to himself” but what is the function of sin?
No, “aige” means literally “at him”, combined with a form of “tá” in any form (i.e. “níl”, “an bhfuil” etc) means “he has”. “Sin” is not directly in the translation they gave but it means “that”, i.e. that one there. If you wanted to get slightly more literal, the translation should really read something like “That man/person/thing (it isn’t specified) thinks nobody is any good”.
