Seven words that set you free.
"I don't have time for this crap."
When you're stood up on a date? "I don't have time for this crap."
When you're in a shitty meeting thats going nowhere and there's a mountain of work to do? "I don't have time for this crap."
When someone - anyone - is a half-hour late for a meeting or drinks or the like? "I don't have time for this crap."
Remember these words. Your life is your life. Your time is your time. It's for you to enjoy, not for others to mess you around and waste.
When somebody - anybody - fucks you around, in whatever way, just remember these words: "I don't have time for this crap."
Make no mistake: it is crap. They are showing you with unconscious malice that they do not value you. In the slightest. Otherwise, they would make the effort for you (or at least give you an early heads-up if something major goes wrong).
Once you recognise this behaviour for the deep disrespect that it is, you should make it a simple corollary: that you have no time for them either.
Don't make time for them, don't feed their habit, don't bother to be more than polite with them if you can help it. If they say stuff along the lines of: "We should go and do X!" Just say "Yeah, doing X sounds great!" Then simply do nothing to arrange X. Don't even mention it again. It (and they) are not relevant.
Understand, these people are just using and abusing you. You owe them nothing. So give them nothing.
Next time your "friend" or "date" flakes or cancels late with a lame/pathetic reason or no-shows, just say to yourself: "I don't have time for this crap." If nothing else, it filters you down to the true friends or girlfriends - leaving the rest of your time for yourself.
Seriously, these people are as common as fucking dirt, and a damn sight less useful. With dirt you can at least grow something in it. So say it brutally and upfront if they have the nerve to ask for explanations: "I don't have time for this/your crap."
This works exceptionally well when said to a narcissist, especially hanging up on the phone immediately afterwards. Because by extension, you are saying that they are crap also. It gets them in a tizz: just remember to ignore the crap that they attempt to sling your way. It's just crap, and you don't have time for it.