Well let this be my introductory post here.
I think it is never appropriate to comment on someone else's play in regards to how it might have affected you or the dealer. If you are playing relying on everyone else to do something, then you are doing something wrong. Just play your cards and let everyone else play their cards.
I will usually intercede if someone tries to bully someone at the table. It is just rude. It doesn't matter if it is the right play or the wrong play. Giving unsolicited advice should be done with extreme caution, providing unsolicited insults should never be tolerated.
Or you could just call them out the next time you lose a hand because of something they did.