Do you tell friends when their new love is wrong for them?

If your friend starts to date an ass hat, are you fast to tell them he/she is wrong for them? Or do you fear your assessment will bite you in the ass?

I never did voice my opinions on this until later, and that was usually in response to concerns that they were already having.

I generally keep my opinions to myself.

I did that twice. Told him she was just along for the ride (he had a successful family business) and yada yada yada...it basically killed our freindship.
Some 5 years later I run into him at Target's with a kid and no her? Tells me she was last seen in a bar somewhere hanging on a guy 25 years her senior with money to burn. Said she didn't like the domestic life and responsibility of family and left when he refused to participate or finance her weekends.

Another was my brother who hooked up with a psycho who later tried to poison him and the kids. She was experienceing the munchausen by proxy shit. He found out his kids had been seeing 20-30 different doctors over the past 10 years. He then discovered an huge cache of outdated meds she had taken from the hospital pharmacy where she worked 3rd shift as a LPN. When he took them to his lawyer, and learned what their side affects were, he realized the side affects were what he and the kids were all experienceing for years including tunnel vision,and dizziness.
Prior to that she had stuck herself with a needle she found at the hospital that was contaminated with parvo or something while she was pregnant.
When his son was born with all types of intestinal and genital problems, she confessed to the needle incident saying she was hoping it would have caused a miscarriage--that was as started his looking for other signs.
Even after the divorce, he refuses to acknowledge my comments and will not talk to me...

I have a dear friend in a very bad and maybe even dangerous relationship. The most I have ever said was "How much longer?". Unfortunately she has a very strange personality and about the only men she attract are the ones where she can be dominate in the relationship. I love her to bits and couldn't live with her. The latest of the 3 relationships she has had is in its 10 year. He is never sober any more and refuses to see the problem. Then when he gets downright slobbering drunk he accuses her of cheating on him with any men in the apt building they live in. I've told her he could become dangerous she says by then he is so drunk a good push would take care of any ideas he might have. Too bad too because sober he is the sweetest man you would ever want to meet. Unfortunately we haven't seen him sober in years.

I might make a comment, but I don't get involved in other peoples relationships.