Threaten low-level violence (not on her though, duh) knowing full well that the only thing you have been able to hit correctly during the entirety of the relationship was a) dat ass and b) a spider, once.
Delete her from every social media outlet.
Block her on Twitter for “spam” because you have a loose definition of “spam.”
Delete her phone number…
… after sending her a series of awful text messages describing how you’re not going to mail anything of hers back.
When she replies, say “Who is this?” because you deleted her number ten minutes ago and have selective amnesia.
Forget all of the good times and only remember the bad.
Also super casually walk a different way when you see them coming, pretend you didn’t see them, and then trip on something large and completely avoidable. Also have conversations w/ their friends in front of them while ignoring them.