Earlier quoted context omitted.
> Will bring it What if they say yes, and then you spend time bringing the bbq equipment to the workplace (although you didn't want to) and then your manager wonders "what are you doing, this'll set of the fire alarm", and you say "the others wanted to try this"
Take 5 min to run it by your manager. "The microwave is broken so we want to being a portable grill to make lunch with Tomorrow." If your manager has objections that's evidence it was a bad idea. Maybe it becomes a company tradition instead to have a hill day instead though?
You're just pushing responsibility for saying "no" onto someone else. I would look at the concept of "ruinous empathy" - sometimes being too facilitative and not giving feedback isn't good for anyone.