I want to go to Egypt, Cairo specifically, but I hate people getting all up in my face.
I've been to places where they approach you and bother you but will leave it you tell them you are not interested. I heard in Egypt they will insist even after you tell them to go away and I'm worried I will end up headbutting some Egyptian seller/scammer and get into very serious problems.
There are many stories of tourists not being prepared for the environment and culture of their travel destination getting into serious trouble.
If you are worried about headbutting someone I'd vote for not going. The local authorities will most often be on the side of the locals in many countries.
If Egypt is your first northern-african/middle-eastern country to visit it might be tough. I'd suggest Jordan or possibly Marocco.
I saw a guy recently wearing both a scowl and a badge that said 'please be kind to me I have autism'. That might work to some degree. Maybe replace 'have autism' with something more appropriate like 'have difficulty restraining myself from physical violence'.
It's not that I have a problem with restraint is that if I have to tell a person 3 or 4 times to back off and they keep pushing me into a metaphororical corner I can lash out.
I never had any problems with violence before other than the normal teenager bullshit because I just remove myself from the situation, but I know myself, and I know of I'm encroached on I will probably lash out.
Everyone else here has already given reasonable suggestions, so drag will give you a fun suggestion.
You should learn to swear in Egyptian. That way, you can tell people to fuck off. You won't have to use violence to get your anger across. You could learn some really vicious insults about their mothers, too. Just make sure they're the kind of swears that get people to go away instead of starting fights.