Shitting bricks?

Quote on Quote from someone:-
"Look at GJ,study so much,no life, no girlfriend no friends"

I LOL-ed Hard at this!

On another note,I was at 4chan message board and i asked a question because theres was this very common quote:
What does shitting bricks mean,or is it an expression for being scared?

The entire list of replies here,each line by a different person:

"It means you'll shit your pants so much it'll come out in bricks."

"its a serious medical condition my grandfather died of."

"It means you shit bricks instead of real shit. Actual bricks come out of your ass for no reason. Weird, huh?"

"should there be any signs if I'm "shitting bricks"?"

"When a slew of coarse, cold, hard rectangular objects are slowly and painfully expelled from your anus."

"That's not funny, my brother died that way."

"My grandfather died in the holocaust :( He fell off a guard tower."

"I built my house by shitting bricks"

"It's cuboid not rectangular:p, and the guard tower joke is as old as hitlers ashen residue."

"An expression used all the time here, yet I not once suffered it."

"Constipation can be fucking painful. But never once have I released a house brick from the pits of my anal caves."

"It means this.

As well as these i found too
"You will shit Bri/x/"
"I work nights, sleep during the day. Please post a creepy thread that makes me shit such bri/x/s that I shant be able to sleep even in the light of day. If you do, I'll give you a dollar. I promise."
"can some please show me whats weird about this that makes it bri/x/ shat worthy?"

Click on the pictures to enlarge them.