I interned with my school's IST (Information Systems Technologies) Department and have converted it into a summer job. I love the feeling of showing the teachers their stupid mistakes. This was my favorite call:
Teacher- "Yes my, keyboard isn't working! It won't put in anything I type!"
"Is it plugged in?"
"I don't know..."
"Okay, pick up the keyboard and stand up."
"Now take ten steps backwards."
"Did the keyboard come with you?"
"It's not plugged in. Is there another keyboard around the computer?"
"Wait... Oh! Okay, this one works!"
"Very Good. Goodbye."
Have you had any of these hilarious Duh moments like me?