Is it just me?

I find it rude when:

I'm in the company of someone, and that person's friend or acquaintance walks over (whom I do not know), and I'm not introduced. Its like I just stand there awkwardly, sometimes I just introduce myself to avoid an awkward situation but come on now, have some courtesy.

I have plans with somebody and that person cannot follow through with the plans, and he/she fails to let me know that he/she cannot make it.

People talk negatively about someone else to everybody but that someone.

I send somebody a text message, and I know that person read it, but he/she fails to respond.

People do not say thank you when I hold the door for them.

I'm talking to somebody, and another person walks over and rudely interrupts, by asking that person a question.

This list is under construction..there's more that I find rude but its not coming to me this moment.