Dark_5.0....Thrifty, along with most other rental agencies have insurance on these cars....and it's no big deal to have 1 of their thousands of cars breakdown... It's a little different than your mechanic taking your ONLY daily driver out and blowing the thing up. They're just having a little harmless fun. If Thrifty had a big problem with this they'd probably go out of business, but they thrive. So one of their cars is broken from doing this...big deal.
Back in the late 60's there were things called Rent-a-Racers....Hertz used '69 Mach 1 428 CJs to rent out to people to take them to the track....how many of those do you think were damaged? I'm sure just about all of them were in some way...
If this was their wife's mom's car, it would be a different story...but it's not....so it'll be ok man....