Hello 
I'm more of a lurker than a poster, but I need advice on..well, on standing up for myself, so who better to ask than you lovely MNers. 
Without going into detail (because it's quite a trivial issue really), I'm getting sick of some people in my life expecting me to be permanently on call for whenever they feel like interacting with me. We do have a regular time to meet up to get something to eat, but I've been left hanging one too many times only for them to turn up an hour late and expect me to still be there waiting for them.
I want to make it clear that I'm not a doormat, that I'm not willing to accommodate them messing me around time-wise, but I'm not really a confrontational person. I also struggle very badly with social anxiety, and while I'm doing my best to overcome this I still struggle with confidence issues, and I don't really feel like I'm worthy of asserting myself. 
I'm still a student, and I don't want my whole working life ahead of me to be defined by me not being able to stick up for myself when I need to. Yes this is trivial, but if I can sort this it'll be the first step towards being a lot more confident.
I'm sorry for the dull and quite trivial post. I'm happy to elaborate more if needed (I'm not being vague for any reason other than to not bore you!). Thanks. 