That is funny.
Sadly, It probably happens a lot. But people know better than to post it.
I get pissed when i put a small scratch oin something I am working on. That is inexcusable.
Should the friends pay for a new ECU?
Depends on the prior conversation IMO. If the guy owning the bike said he wanted a Fender Eliminator but was worried about it and the buddy said he will take care of it. He better take care of it.
If one dumass asks another dumbass to do something with out researching himself.... not sure dumbass #2 owes Dumass #1 anything.