With food, well, at our table at the Melbourne Mega-meet (queens' birthday) I asked if people would mind not ordering grain-fed meat because it's ethically bad (given the amounts of antibiotics fed to the cows to actually keep them alive after changing their diet from pasture to grains - it's horrid).

Great ideas with the post-it notes!!!! A friend of mine (in a wheelchair) carries pre-printed notes and a tube of super-glue to stick on the windows of rude people in carparks!
Do you mean feedlotted beef? Because there is a huge difference to feeding your cattle grain in a regular farm situation to feeding cattle grain in a feed lot situation. Not all grain fed beef is evil

And as for using super glue, well that's vandalism and I have a very low opinion of people who vandalise stuff, even if it is to get a message across. If that were me who found something SUPER GLUED to my car I would be absolutely white with fury.