The current trend in government seems to be to do whatever they want because to do otherwise invites (or fails to prevent) terrorism.
Here are some things that might be done by terrorists which governments should consider banning:
Graffiti – could be used by terrorists to mark locations for attacks or send messages to sleeper cells. It’s already illegal but that doesn’t seem to stop anyone. Send the graffiti “artists” to the same places that they send illegal immigrants.
Spitting in public – could be used for biological warfare (it’s effective at spreading disease).
Putting feet on seats of public transport. Shoes have been used for smuggling explosives on to commercial airline flights and could be used for bio-warfare.
Sticking gum underneath chairs. This is an obvious risk for bio-warfare.