Smoking, drinking, self mutilation, laziness, over eating, under eating, using recreational drugs, not exercising, gambling, intentional sleep deprivation, and negative thinking are all self destructive habits.
Self-destructive habits come in many forms. They could be as obvious as cutting yourself and other body mutilation to less obvious behaviors such as smoking cigarettes and drinking alacohol. Other self-destructive behaviors include wreckless spening of money, unprotected sex, or engaging in otherwise risky and dangerous behaviors.
Overeating or starving yourself are good examples. Sexual self-injury, entering meaningless relationships left and right, drug use, etc. Basically self-destructive habits are any behaviors that are harmful to you, especially if you are doing them to avoid dealing with insecurity, past trauma, or other issues.
Some self-destructive habits can be subtle and are not always entirely detrimental to our overall happiness or success. For instance, you may find that you don't quite study long enough to get an A on an exam, or you aren't quite considerate enough during arguments with your significant other. Other habits may be more detrimental, such as smoking or drinking.