What does it mean when french people leave this comment into your blog: mdr?

It's the French equivalent of LOL. It stands for ''mort de rire'', which literally means ''to laugh to death''

Well, you must first consider one's circumstances when they are leaving "mean" comments on the Internet. This "mean" commenter may have just broken up with his/her mate. Or a close relative of his/hers just died. Or he/she could simply be having a horrible day and is extremely irritable. The list goes on. As very emotional and expressive beings, it's natural for any person to let it show. It is venting. Maybe he/she would scream into a pillow. Or workout at the gym. Or leave "mean" comments. In no way, does a simple comment characterize a person, especially on the Internet. That brings me to my next point: the Internet provides the user with a blank slate. Like a tourist in a foreign country, they have the ability to be whoever they want, without any threats or consequences to their life in reality. The Internet acts as a facade for an interested user. "Maybe I'll be intellectual today" as he/she skims through a thesaurus. "Maybe I'll be a 12 year old little girl" said the 60 year old pedophile. "Maybe I'll be mean today" said the shy, math whiz who never has a chance to shout vulgarities and criticize others in reality. True personality cannot be expressed through a simple two-line comment reading "Suck it" repeatedly. With that, take such comments as a meaningless joke. Because they are.

mdr = lol

mort de rire - Died of laughing