As humans we primarily make time for what we really, really want to do over what we should. Before getting angry at someone for being late take a step back and assess the situation objectively. The person may have been late because they probably weren't that interested in seeing you, they may have had something more interesting to do or had an interesting conversation going on.

Walk away after 15 ( or 10) minutes because you should have something better to do with your time than wait around hours for someone, right? There needs to be a negative consequence of the bad behaviour and it should be communicated through your actions rather than your words. Words will always fall on deaf ears.

I remember a friend who had a problem with a very tardy friend from one of the warmer EU countries and started to leave habitually after 10 minutes of tardiness. After a couple of times he got the idea and even started arriving early to the meetings.

You don't lose anything by doing this. It's a good strategy since it reveals the nature of your relationship with that person. If you don't like the revelation, fix it in a socially intelligent manner or exit the relationship. ...