"Shitbrix", "Shitbricks" or "Shitting bricks" is when you are suddenly startled or afraid...So afraid that you could "Shit a brick".
"Shitbrix" is also a website- shitbrix.com
If a wasp suddenly buzzes past you, you may be suddenly terrified and shit a brick.
If you're watching a horror movie and something scary happens, you may scream and "Shit a brick"
If you visit the website shitbrix.com and you find something creepy in the pic, you may go "Holy SHITBRIX!!!!"