Usage when a character does something stupid with a lack of foresight and is about to be punished for it. Foreshadowing of impending doom, usually comedic (to the viewer). May apply to the viewer if the cause can be reasoned out. If the character is currently being punished or is suffering the aftermath of it, put it in Told You Not to Do That instead. If the character is about to meet a bad end but not through their own stupidity, put it in Impending Doom instead.
It is not for simple you gonna get raped or badass posts, but more of an "I wouldn't be doing that if I were you" feeling. The distinction here is that the victim has obviously brought it on him or herself. It's not someone accidentally stepping on a mine, it's someone about to gleefully smack a mine with a hammer. Some guy receiving a death glare from a knife-wielding yandere girl is an awful situation for him. It's only Digging Your Own Grave if he's sitting in front of the fridge, eating the last of her favorite desserts.
If the victim could have avoided it by not being stupid, it's Digging Your Own Grave. Bonus if the post causes the viewers themselves fear.