The best way to get back at an ex involves personalizing your payback. It's one thing to post a bunch on social media about how much fun you're having and how much you've moved on since the breakup. It's also one thing to block someone outright. Those options might be petty, but they are also uninventive. What you really need to do, if payback is necessary, is to find something niche about your former partner and see if you can use that to your advantage. Now, payback is not pretty and it's not…