Reposting (with minor edits) something I wrote in another comment a few days ago:

Cars force communication that is inherently anti-social. If someone is genuinely sitting at a light too long, you honk at them. There aren’t a lot of other good options. But even a honk sounds aggressive. You could be as polite a person as can be in any other situation, but making the completely reasonable choice to honk at them makes it sound like you’re calling their mom fat.

When this happens to me, and the guy ends up pulling into the same parking lot, I tend to avoid any other contact, even if it’s just walking by.