Vegan ambassador chiming in:

I wonder what the mess from a water balloon full of e.g. Just Egg looks like.

Milkshake is piss-easy, though. Unless you’re in a bigger city, you’ll be lucky to find a proper milkshake purchasable in the wild. However, you can totally make one at home and put it in a disposable container; a homemade plant-based milkshake is about as hard as a homemade dairy-based one.

Especially bearing in mind that deliciousness is not necessary.
Deliciousness is always necessary. You think you’re going to spark change when that neo-Nazi gets a little milkshake in their mouth and doesn’t taste sweet, creamy, ice-cold goodness with a hint of pistachio – transporting them back to the tin roof sundae their parents got them from Ronnie’s to make their boo-boo all better after soccer practice? I don’t think so. Slacktivism like that won’t get you anywhere.