There's really no correct words to tell gamblers if you want them to stop it or control their gambling problem. Sometimes, they do not absorb what you say and will just ignore it. I think the best method is to show them how much they are losing over how much they could've saved if they didn't gamble their money.
Less talk, more work. If you are both men, you don't like talking, and you don't want any advice from another men. It's better to just show them instead of becoming the Dr. Phil for them.