I love running into someone from my past. One time, I was walking in the West Village, and a guy I did Legally Blonde The Musical with when we were 17 got out of an Uber and ran up to me in recognition. Those interactions can be so fun because you quickly get to see what they are doing at that exact moment, maybe where they are living and what their job is, and that’s it. It’s fun running into a random past acquaintance when the interaction takes three minutes or less, but if they try to tag along with what you’re doing or push it to hang out with them in the future («We should totally catch up some time» is usually a lie, Thank God) it ruins the novelty of meeting up randomly by happenstance. There are always exceptions, but for the most part, that is my rule.