What self-destructive behaviors do we knowingly engage in? Why do we believe the behaviors to be self-destructive in the first place? Why do we do it, even if we know it's bad for us, either short-term, long-run or destructive to others in a way that comes back to us?
Don't feel like you need to promise that you'll never do it again; those kinds of promises never work. However, if you'd like to share any efforts you're making towards changing the behavior in question, I'm sure it would be productive to do so.
Also, if we each make it a point not to criticize others' weaknesses (which coincidentally is a behavior that this thread could apply to) then we won't have to fear criticism from others, making it easier and more likely for us to share our weaknesses. You know. Bonding and acceptance and such.