Don't be a "flakey friend". You're better than that.

Since I am well and truly sat on my cactus today, I'm going to have a little rant.

As a child, I was always told that you honour your original engagements. It doesn't matter what other "offers" come along at a later date- if you've accepted an invitation (Formal or informal) then you're already busy.
No ifs, no buts, no coconuts.
If you don't want to do something, then you politely decline at the time of offer ("Sorry, it's not really my thing but let me know if you're doing something that isn't sky diving/bikini waxing/bog snorkelling etc") you don't agree (Or even worse say "Yeah maybe") and then just not turn up/ cancel on the day/ accept a different engagement and screw everyone else around.
It's rude.
And it's what you're basically saying to that person who originally offered you a social invitation is "Yeah, your friendship is worth so little to me that I don't feel bad for wasting your time".
Or worse, this is an assumption that I am so desperate for your friendship that I will tolerate being dropped like a hot potato. I am afraid that this is not the case.

Obviously I understand (Only too well) that sometimes things happen that are outside of your control. You can't help being sick (Although hangovers do not count, because you can help those), having a family emergency, having a flat car battery, the weather or the traffic.
If you know you can't make something just be honest. As soon as you realise you won't make it. That way you don't waste the other persons entire eventing/ weekend.

This is something that really frustrates me. And probably a good portion of the population. I'm a busy person. If I'm not doing X then I could be doing Y*. But if I have to wait for an hour for flakey friend to finally text me and tell me they're still in Liverpool (Or bed, or too sick, or they're out with so-and-so or they have a date so now they can't make it) Then I'll no longer have time to do Y.
I'm not flakey. If I say I'l be there, I'll be there. With bells on, 10 minutes early and I might even bring snacks.

(*Y is some kind of task or chore like going to the bank or getting my eyebrows waxed or hitting the gym- Y should not be another social engagement as X is already agreed to)

I would genuinely go to the end of the earth for my friends. I've flown all over Europe- even as far as Malaysia and will be going to Australia  to see friends working abroad. I've driven 100s of miles in the middle of the night because people have needed moral, emotional or physical support. I genuinely spend a fortune on postage of parcels and letters to cheer people up or to celebrate with them.  I really do expect that to be recipricated in that person's own little way.

I think that flakiness annoys me especially (It's a cardinal sin in my book) because I'm pretty introverted (I know, you'd never have guessed, right? All that Physics and passive aggressive blogging).  I choose my friends very very carefully so I feel it very keenly when they let me down by not meeting my high expectations of them.
That's not to say I don't like people.
I'm a bit socially retarded but if I was a SIM, When I meet someone new they always start out in the middle of the green "Like" bar.
I like to meet new people and have new experiences, but I am often let down by my new acquaintances (I guess they haven't figured out how many rules I have about al this "Going out and having fun with other people" stuff).
If I've gone to the effort of making plans with you it means that I like you enough to initiate you into my friendship group. Frankly that is quite an honour. The number of people who's opinions I'm bothered about I can count on my fingers- Not many people pass my initiation. I'm choosey, I won't just spend my free time with anyone.
But flake out on me a few times and you'll not be getting very many invitations as you've made your opinion of my value to you perfectly clear.

I'm not saying I have to be your number 1 person. I'm not saying you have to accept every social engagement I offer you. I'm saying- "If you told someone you'll be there, be there" Be honest. Be a better friend. Value the people around you, or they won't be there for very long.
They might not always be cool or sexy or super exciting. But they're constant, consistent and they care enough to invite you to spend their precious free time doing something that they think you'll enjoy.
Don't mess people around. They deserve better.

I'm pretty certain most people feel the same way!