Sorry for the stupidly specific question. This is definitely not something that just happened to me… Anyway…
So what do you do in a situation like this? Do you walk slower to avoid any interaction? Reach them and greet them? And if so what do you do afterwards? Just walk together? lol
If it’s a close friend I’d approach them from behind and do something silly like poke them on the opposite shoulder or grab something from their hand (that’s not their phone, wallet, or similarly important). Then I’d talk to them as I normally do.
If it’s someone I know reasonably well (old classmate from college or colleague) I’d approach and call out their name in a clear but not too loud voice; “Hey [name], how’s it going?” and ask some basic questions like how they’re doing, what they’re up to, etc. Mostly to show that I care enough to acknowledge them, because while it might be a short term pain for me, it can help a lot in the long run to maintain these connections.
If it’s someone I’m acquainted with but don’t know too well I’d pretend not to see them, maybe even slow down a little to create distance. This could also apply to the above if I’m really not in the mood to talk.
I feel like this is the correct answer, meaning that it is a nice and easy to understand explanation of what is generally expected and accepted.
What I actually do is everything in my power to not be seen, but otherwise an enthusiastic “Hi! :3” without slowing down at all so they don’t think I want to actually talk to them, lol.
I feel that last part. Recently I ran into a colleague with his wife (whom I never met). I said “hi” but tried to look like I’m in hurry and just kept going because I have no fucking clue how to deal with that situation.