I wanted to punish him somehow by sending another transaction with an indication in the notes that this is a fraudulent address but I think it's stupid...
Sending him more money will be a stupid idea. There are sites where you can tag scammers addresses. Like :
https://bitcoinwhoswho.comIf this is a bitcoin tx then sign a message using the address you sent the coins and tag his address with the reference of this thread. This may help a bit to aware others.