Ya know in total I think I've voiced "on your left" more on escalators and moving walkways than I have an MUPs.

On MUPs I'm less prone to get annoyed by a meandering cyclist poking along enjoying the daisies, as I'm that person myself at times. On an escalator I simply want to say "Move your ass and your luggage to the RIGHT and stand single fricken file. Not sprawled across the entire width of a shared space."

(Sorry. Just dropped my mom off at the airport.)