It really is a question of being sensible and considering the consequences of what you are doing. If you are flying ultra low across crops you will do little harm, but what about the horse rider that gets her horse startled, falls off and breaks her neck, or cattle or sheep stampeded into wire fences.
If you are over a built up area, when the engine stops can you land clear or will you crash into the local primary school, just like driving if you cause death by dangerous flying you will go to jail, yes it was an emergency but why were you there in the first place. Get your thrills by all means but don't put others at risk or even annoy them.