This
excuse is based on playing with the
subconscious. I use this with teachers at
school with fairly good effect.
"You're 4 minutes late."
"Sorry Sir, I left the oven on"
Now at 8:55 in the morning, there's no logical reason for any oven to be left on. The boss/teacher will go inside, with the visual indication of his eyes looking up and to the side. This is your cue.
"Don't punish me, I'll sit down and won't be late again."
Now his/her subconscious which has been trying to catch onto some form of logic will grasp your statement and will agree to it, no matter what the teacher wants. There is nothing else for it to do. It must happen.
"Sit down and don't be late again"
I win again...