The universal phone number used in examples, so as to imply that it is not a real number. It is almost entirely understood that the number is not to be called, as it is "not a real phone number" If it is a real number, I feel bad for the guy who has it.
Used by Chinese speaking people, more commonly girls to denote crying, or sobbing. The Chinese word for five is Wu, therefore 555555 translates to wuwuwuwuwuwu. Which sounds like sobbing
555555555555 is a curse word not very commonly used, but when it is used it is 99% of the time Dota 2 players. The word is most commonly used by plebs who love to trash talk other players for various reasons.
What 555555555555 means is still unknown, but most peoplebelieve it means "Idiot dog".
An Egyptian insult, pronounced like CHHHHHH (like the grunting of a pig or a very great snort through the nose). Its a pretty bad insult and u can often expect a fight afterwards, exept u put an A7A afterwards, then it indicates that you are surprised.
Its written 555 because the 5 looks like the arabic letter خ which indicates the sound CHHH