Especially infuriating when the other person is in a very different time zone. I once worked on a project with a partner company in a time zone 10 hours ahead of mine and it was common for trivial things to take days purely because the other person insisted on typing "Hi," waiting for my "Hi, what's up?" response (which they didn't see until the next day since our hours didn't overlap), and then replying with their question, which I didn't see until my next day. Answering the actual question often took like 30 seconds, but in the meantime two or three days had gone by.

I came to believe they were doing it on purpose so they could constantly slack off and tell their boss they were blocked waiting for my answer.