A party might be a different thing, but when you are meeting one or two people, the expectation is that they will not leave you standing around on your own for any length of time.

This is a sign of bad time management on top of rudeness.

I have known people who were continually late, so I would always tell them 30 minutes before I get there. Effective technique.

Things were worse before mobiles of course, I would wait for 10 minutes, and then head off. This was an accepted rule among my friends.