(v) when a person intentionally does something that causes emotional or psychological anguish, such as constantly reading a recent ex's updates on Facebook, or listening to old speeches made by speakers they vehemently disagree with. Phrase is derived from the happenstance of someone having a sore tooth, which they keep purposefully poking at with their tongue, keeping the pain constant, while simultaneously exclaiming "Ow!".
ex 1: I've spent the whole afternoon looking at my ex's photos of her and her new boyfriend at Disneyland. Just poking the tooth, I guess.
ex 2: (person one): "You hate that guy! I've been listening to Rush Limbaugh on the radio for hours today, and it's just been pissing me off!"
(person two): "Why are you poking the tooth like that? Now you'll be in a bad mood all weekend!"