Blog is short for "web log" a popular way to journal your life online for everyone to read.
When you're with someone and something blog-worthy happens, then you say "Blog It" to them. It is a suggestion for the other person to note the incident in their blog.
Neil: "I can't believe that just happened."
Chad: "Dude, you have to Blog It."
Quick and easy way of verbally owning emo kids, whiny bitches and/or just about anyone who complains so much, they make you want to choke a small animal then shove it down their throats. Can be used for all degrees of whining and in conjunction with other anti-emo send-offs like "cry more", "\cry" and "don't cry, emo kid".
Emo kid: "People just don't get the pain I've been through since my 14 year old girlfriend dumped me. The world sucks, my soul is crushed and I can't go on-"
Victim of whining: "Fucking blog it, you emo fag!"
Kid 1: "Man, this class sucks."
Kid 2: "Blog it!"
An expression of distaste for an event.
Basically, a sarcastic, rude way of saying, "No thanks, I do not wish to participate, but tell me how it was."
Blake: "Hey, we're going to go to a club in Hollywood, wanna go?"
John: "Blog it."
Blake: "You jerk."
When you see something that is worthy of going on your blog.
I see a funny/interesting/cool/wicked picture on the internet and i shout "blogit!!!!"