I attacked a pirate ship the other night (it was already busy with another foe) and fought it for 10 minutes.
My buddy just watched - he didn't want to jump in until the shields went down - he said I was on my own because he was tired of me getting him killed.
The shields went down, he watched for another couple of minutes - my hull was at 36% when he finally engaged.
The pirate immediately turned on him, blew him up, and within 5 seconds was destroyed leaving me with 250K in credits.
He's died to getting sucked into a sun, pirates, Federales, stations (for smuggling), and running out of fuel.
Sometimes if you want to grief someone there is no better way to do it than by being his wingman.