Is it time to start calling out bad cyclists?

undertaking people that you're not riding with is rarely ok. and you should at least say something before you do, like 'coming up the left' or 'on your inside' or something. i wouldn't expect people to check their left shoulder before moving in to the kurb if they were in the left hand lane already

it's best to never undertake, usually so you can get into the habit of overtaking instead.