I was taught from day zero that if the engine(s) are running then you should behave as if you are going flying.
I had a stand up shouting match (he started it) with an engineer who refused to strap in for a ground run. We waited until he did. it took 30 minutes would you believe?
He argued for half an hour about why he didn't need to strap in for an engaged ground run. Just why!?
I showed up once for ground runs at a maintenance co in Europe. The aircraft was barely assembled and there was a plastic box where the pilots seat should be. I demurred and asked for a seat. Half an hour later i was called back - there was a seat.
I went up, shook the seat and it came loose in my hand. I laid it on the tarmac and flew back to Uk.
I did a ground run the other day and at the end the engineer said... "did you really need your life-jacket on?"
Fair enough but i treat every start like it's the real thing - good habits may save your life one day..
As for listening to your phone or an ipod during aground run... As 212 says i try hard never to say "i would not do that", but " I would not do that"!
Very sad indeed