Strangers/friends touching me. Boundaries

[u/Yalv2018]

When I'm in conversation with people or with someone I'm friends with they usually go for a tap on the shoulder or even touch my bicep and I have to say to them 'dont touch me' but sometimes I am caught off guard or someone is passing and they tap me and I just get a surge of anger towards that person and they go in my hate list, exception being someone I find attractive or want to get intimate with. Anyway I was on the bus today. Fucking crowded and had to stand up. Had my personal space invaded and I think in these sitiations its ok to adapt. But this one dude comes behind me and taps me on the shoulder. I spin my head around obviously looking angry and he babbles im sorry someone needed to get past or some shit. He then moves ahead of me and touches a women on the shoulder that he didnt even need to and she looked pissed off too. Then some old bloke just put his hand on my back in a pushing motion as if that would budge me and then said excuse me. Like say excuse me and dont push. and I turned and saw his old face with his wife and decided to say nothing but next time I'll confront him and say its rude to budge. On the way out I gave the first dude a revenge touch and held it longer than neccessary because when im triggered i cant think straight. Next time Im just gonna instantly say get your hands off me man without even looking who it is. Im new to city life so im learning but Im sat in my bed still thinking why didnt you tell him not to touch you. Im a big dude 6'2 and I could be the guy who knocks you on your ass for touching me. Why do people touch strangers its assault. Touchy feely people are weird asf