Why people don't think that things that they write/speak can hurt others?

well i was boring one jour and i had the birthday 2 so i posté in this club i have birthday today just because i didn't know what to do other and i get some commentaires like this:oh happy fucking birthday (maybe he thinked i was an attention whore) and about 2 days later i posté an another question: I know that this was posté 1000 times before but.......post something funny....and they started to make irony with me someone wrote:
something funny (just thad he/she wrote just that maybe he was laughting with my sentences)
ok i agree my english spelling is not good but doing mistakes it help learning ou they used sarcasm like i was so dumb just please stop maybe people will use sarcasm again toi maybe will say:ok girl when i will answear a question in fanpop first i will see who is asking and than i will decide if i have to use irony ou not...I know that i am 2 sensitive but PLEASE stop!