A derogatory reference to a person who writes e-mails using all capital letters. Combining elements of the phrases CAPS LOCK, signifying capitalization, and RETARD, signifying a person of low IQ.
"Did you get that e-mail message from the boss? What a capstard."
I was walking around work tonight in circles, not doing anything in particular and someone called me Castarded and I laughed my ass off and got out of work 20 minutes late bacause I was laughing so hard.