No matter how badly someone might break your heart, after enough time passes, we still aren't ready to burn that bridge. If you saw them again, you would still be somewhat cordial and polite. Just give an honest honk and wave. Make him/her feel like an ass.
"She really broke my heart in two. If we drove side-by-side on the highway, maybe i could honk and wave." - paraphrased from a Limbeck song.