Cause being childish on the internet is the new thing these days. It is even said adults are now doing it as way to express themselves because they have no real goals in life except imagine the laughs of other people over the internet without experiencing it person to person.
Also 50% of people think they're cool while doing this, the other 50% are actually just complete idiots...
[spoiler]That is a made up statistic...[/spoiler]