i donno buddy, im gonna have to say this is your fault.
and heres why...
i know my friends, i have some pretty good friends, but i would never trust them with my bike unless i was prepared to file with insurance for a totaled bike. burning the tires should be expected. its like giving satan an icecream cone and telling him "hold this for me, and don't let it melt.".
is it wrong what your "friend" did, yea. should you be surprised, no.
i've had my family, my brothers, steal from me, drop my bike, get drunk and try to woo my ol lady (always funny), and yes abuse my motorcycles.
a hard slap up side the head works for the most severe infractions (stealing), but most the time i just hit them in the arm, midsection, or junk, at random (uasually while were drinking) til i forgive them....or in the case of hittin on my gal, we (wifey and i) tease them for years for it.
if your really bummed about your tire, ask him to get you a new one. or you could just punch him in the junk every sat night for a couple months......pa pa pa pa nut tap
what ever you do, dont dwell on it...do something, or let it go.
not like he totaled it.