What are some homeowners surprised to find out that they can't do on their front lawn?

Fornicate.

You’ll have to ask my homeowners association this question. All changes must have a committee approval. Those who don’t comply get sued.
Certainly no boats, cars, trailers. And no trash cans visible from the street. My immediate neighbors are OK but the homeowner association has a lot of SOB’s. I refuse to recognize them as a controlling organization and refuse to pay dues. Been living here for 32 years and never paid a dime of dues. Why give them money that they can use to pay lawyers to sue my neighbors?

Burn a giant cross?

How about growing food on your front yard is illegal in cities across US cities?
https://www.earthisland.org/journal/index.php/articles/entry/local_laws_ban_front_yard_food_gardens/