It's because of anonymity, like they say "None of us are as cruel as all of us."
Also, Rule 20. "Nothing is to be taken seriously."

Wat the fuk did u jst fuking say about me, u little bitch? I’ll have u no I graduated top of my class in the Navy Seals, and I’ve been involved in numerus secret raids on Al-Queda, and I have over 300 cnfirmed kills. I am trained in gorilla warfare and I’m the top sniper in the entire US armed forces. U are nothing to me but jst another targt. I will wipe u the fuk out with precision the likes of which has nevr been seen befor on this Earth, mark my fuking words. U thnk u can get away with saying tht shit to me ovr the Intrnet? Thnk again, fuker. As we speak I am contacting my secret netwrk of spies across the USA and ur IP is being traced right now so u bettr prepar for the storm, magot. The strm that wipes out the pathetic littl thing u call ur lyf. Ur fuking ded, kid. I can be anywer, anytime, and I can kil u in ovr 7 hundrd ways, and thts jst with my bear hands. Not only am I extensively trained in unarmed combat, but I hav acces 2 the entire arsenal of the USMC and I will use it to its ful extent to wipe ur miserable ass off the face of the continent, u little shit. If only u cud have known wht unholy retribution ur little “clever” comment was about 2 bring dwn upon u, maybe u wud hav held ur fuking tongue. But u cudn’t, u didn’t, and now ur paying the price, u goddam idiot. I will shit fury all over u and u will drown in it. Ur fuking dead, kiddo.