This is in the UK? This works both ways, no? I cut myself cuz someone was a jerk and then I can sue and get paid?
Idk, I said I'll kill someone to a police officer while I was at the police station and was never jailed, I have clear criminal record, etc. Don't try this unless you're me though, I don't guarantee the outcome will be the same

. It was still in Poland / my country of origin, wouldn't risk it in a foreign country

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You would have to prove it was caused by the person being jerk for example if you it happened say 2 days ago you recorded on your phone or somewhere else saying this"I cut myself because of what someone said which deeply upset myself" next you would to take photo of it prove it did happen next then you would go to see doctor or nurse to prove it happened and also get some get kind of support all that would need to be done before you do anything legal with it.
You would also have to prove for example if you got medicine for depression or something mental that it made you take more of it or had to take a stronger or new form to deal with the stress.
If you do all that stuff you meet a proper confident Doctor or nurse they should recommend you get seen by some kind of mental doctor who then should guide further on what to do .
If you can prove it like this with the steps I recommended, then you yes could probably sue and win.
You also have to include every judge bit different some are very nice or some are bigheaded or some in the middle so you have to include as well. Each judge has to do the best possible reasoning to workout who is right or wrong which can get pretty complex.
To give you another example lets say man and woman date both get into big arguement anyay lets make it simple man hit her over the arguement now if it was you would consider soft hit then nothing would probably happen but if he did put her life in risk then judge would make him go to jail or charge him or make him go to some kind of angery management class.
He could claim it happened over what she said as a defence which could work for him depending on how he presents or smart his lawyer or her lawyer is for what would happen.
If someone says the following
You fat
ugly
Smell
stupid
weird
strange
That would be considered not rude or extreme, meaning if someone got called ugly then kicked the crap out of someone judge would not pass him for acting reasonably and would consider him overacting so his defence be pretty useless here.
For Kill idea they would have to prove you would do it people say all the time I am going to kill or stab or shoot or something like that but most don't it meaning in order for the copper to prove it, he or she would have to prove you have proven to do something like that or his arguement void.
It's like someone claiming for example karate chop lion so now all the zoos have to guard the lions from the nutter but in order for that to be applied, they have to prove he has an interest doing stupid things, which again be complex unless he has record already for similar things