Question about accidental meeting of an old bully?

What is the reason between physical superiority? Suppose X is a guy with a normal height and being bullied by Y, who is much taller and strong. One thing x can do is to report the authorities that I also know. But what about inflicting mental pain? Suppose y won’t harm physically much, but would just grab the skinny hands of y and look in a threatening way. So how would a person counter attack in that matter? For example X was constantly bullied by Y at the high school and then they parted. Then one day Y sent an abusive mail to X, even though X didn’t do any harm. Suppose one day, only by coincidence both of them had to meet somewhere, be it a mall or a train station. How should X confront Y with confidence? Ignoring is okay but if he grabs your hand and obstructs?

around here in NY (which is in the USA as opposed to other NY's) its called learning how to say/yell ....no. and if the person persists theres a court process called getting a restraining order (protection order) this is a paper that allows the police to arrest the abuser any time the abuser goes against the restraining order...

example if the restraining order is about being in close proximity to the victim and the abuser shows up and doesnt stay for example 500 feet away from the victim, the victim calls the police, the police arrest the abuser.

if the restraining order says the abuser can not write, email, talk to the victim and they send a letter, email or call them or shout out to them the victim calls the police, the police arrests the abuser.

as for confrontations well thats individualized based on what the victim needs are. some invite their abusers to their therapy sessions for a confrontation others write a confrontational letter and there are many other ways a person confronts their abuser. I know someone who sent flowers with a card that said leave me alone my next call wont be for flowers it will be for the police. he persisted. she went to the police station and filed a report, went to court got the restraining order and the next time the guy showed up she had a neighbor keep him busy while she called the cops. he's now in jail.

So, just reading this is very confusing. It sounds like you are trying to take a real life example and make it hypothetical to get opinions on what is right/wrong in the situation.
Bullying on any level is wrong, and leaves many mental scars that don't go away quickly, like physical ones. Perhaps you might add a little more information, and less x's and y's and we could support you a little more?
One thing I'd like to add is that bullying is about power. It can be done by any size of person to any other size of person so long as they can assert power of some kind over the other. Therefore the only way the bully can still hurt someone is to still have power over that person. This includes knowing that they are causing emotional reactions in that person. One of the most pathetic things in the world is to see a bully who has lost all their power over others.

Okay I understood. Then I will tell aboutsome people who always want to assert power by physical strength. Once I knew a guy who would always use swear words and was proud of ‘a self-made’ guy. I don’t have anything about any class still he took proud about his working class roots and used to belittle me as I had a better background.
I have noticed people that if they analyze you are a weak person, then they would try to assert power. There is also a possibility of misinterpreting your politeness too. These all stuffs are related to social backgrounds. I guess thy always thought I was an inferior person, as I am a skinny guy, no broad shoulders or abs, as I had a some diseases in my childhood. They took this for granted and tried to bully me. I have never went for a direct fight against anybody but even if I did, I would have failed too. I would often think about people who are weak and still retaining their confidence against anyone.

Actually, assault is also the threatening of harm and not the actual physical attack. If he actually hits you, then it's caleld battery.

So, if he's threatening you in an e-mail, that's assault. Because you've already said he's obviously bigger than you and could carry it out.

You can read more here:
Assault and Battery legal definition of Assault and Battery. Assault and Battery synonyms by the Free Online Law Dictionary.

I was horribly bullied as a teen. I wish I had known about all this back then.

if a person is in the USA each state has their own definitions of what constitutes assault.. example here in NY we have more than one definition ....

Assault in the first degree: N.Y. PEN. LAW § 120.10 : NY Code - Section 120.10: Assault in the first degree

here in NY assault in the 2nd degree is...: N.Y. PEN. LAW § 120.05 : NY Code - Section 120.05: Assault in the second degree

Here in NY Assault in the 3rd degree is....: N.Y. PEN. LAW § 120.00 : NY Code - Section 120.00: Assault in the third degree

we have many more definitions of assault too based on situations...
NY Code - Article 120: ASSAULT AND RELATED OFFENSES

to find out what a persons own country or state stands on defining criminal actions like assault you can contact your local law enforcement or type in your search bar something like ...what is the definition of assault in .... (your location)

If x grabs Y's hands without consent and invades y's personal space then y would be well within his right to knee X where he keeps his crown jewels! after all Y will be feeling threatened by X and has the right to defend himself! At the same time making a loud commotion of shouting go away, no, I do not want you near me, leave me alone, get your hands off me etc. would also help as it will draw a crowd and x will be more likely to be scared off.
bullies only target those who they think are able to be bullied, stand up to them and they often run in the opposite direction.
I was bullied for years at school, until the day I snapped and gave the bully a taste of her own medicine, she kept her distance after that.