I've asked people, friends, coworkers if they knew that corporate mandates those messages on cups. I have yet to meet someone who knew before I told them.

Telling people you're boycotting starbucks does nothing I've found. Tell them corporate mandates those fun messages and I've seen many visible snarls at their cups. It's a nice reminder every time someone goes to Starbucks how their workers are treated. So next time you see a friend or family member with one, casually mention it, it might alter their viewpoint a bit!