Both my military background, as well as my Amateur Extra radio licence have taught me a lot of radio etiquette that I don't see being used in ATC/Pilot communications, much of which is spelled out in the Pilot / Controller glossary sadly.

I try to set an example when I talk on the radio, especially when dealing with Foreign ATC... however, I have to admit, the pilot training on radio phraseology in the US is very informal and done in such a way that you learn OJT and you learn by example.

My suggestion is for you to take a learning moment and politely ask the pilot who steps on you to wait before he keys' next time.