Flaky people are the worst. I don't mind in a group setting if people bail on plans to meet up. If you're meeting with friends at a bar for instance, if one person decides to stay home or make other plans it's fine. If you're having 1-on-1 time with a friend and make plans in advance and decide last minute to bail, that's pretty annoying.
As a portrait photographer, it's doubly annoying to have a client back out last minute. I don't think models understand the work involved in making good portraits. I had a model shoot planned for today and around noon I checked in to make sure we were still good to go. Only after I prodded her did she tell me "oh, we will have to cancel" with no excuse or information beyond that. Since this was a planned shoot, I did have shots in mind that I wanted to execute which took time to research to be able to guide the model so that we could nail the look. I had lighting schemes I wanted to employ and gear that I had to inspect, clean, and set up before the shoot today. If professional photography isn't something you can relate to, then consider if you invited a friend over for dinner.
The plan was that you were to cook dinner for this person on a specific date and they would arrive at a specific time. You go to the store to buy the food you'll need to prepare and you consider their tastes, likes, dislikes, etc. The day you planned to have dinner, you begin cooking and preparing their food and maybe cleaning up a bit to make your home presentable. While you're cooking you call your friend to double-check they are coming only to have them quickly dismiss your dinner plans with an empty "sorry, can't make it". You're stuck with food for two, not to mention the time wasted in preparation before you even began cooking.
I guess it's my fault for not taking a deposit to ensure they are at least financially invested. This is what I get for doing time for print gigs.
I'm done ranting.. maybe I'll go take some selfies.