I must respectfully decline your invitation

On Wednesday a couple of the teachers were collecting votes for some teacher union election, and I was chatting with them during a free period: Marilyn, another English teacher, and someone whose name and face I can't remember who I'll call Carla. We talked a bit about teacher unions and how elections get run (they have designated teams to collect the votes, and I have no idea how American unions work). Then Carla starts a new topic.

"Oh! And sometimes we have huelgas [strikes]. You should march with us!"

We went through multiple discussions of teacher strikes during training. There's a long history of grievances about pensions and whatever, and basically we need to not get involved. If there's a strike, we never cross a picket line, and we call our co-teacher and ask if we should go to work.
Also, as Nicole from the Ministry put it, "They're a little water-cannon-happy here." Demonstrations that seem perfectly sweet and peaceful can escalate in a matter of minutes to police with riot gear and people in ski masks throwing bricks through windows.

"Sorry, I can't."
"Why not? It's fun!"
"I'm not allowed to."
"No problem, you can just wear a mask."

(Seriously? This is your solution?)

"No, I really can't."
"If you don't march with us, you can't stay here." (Chile? This school? No idea.)
"I know, I know. But I'm planning to leave in December anyway."
"Aw, you should march with us! And sometimes the police come and spray us with water!"

I don't have to take every opportunity to get involved in the host culture.