Surely, he didn't injure anyone, but he used safety devices without proper authorization. Perhaps equal to someone using fire hydrant just for fun or toying with lifeboat. I don't know what is the proper sentence for this.
That escape slide on A320 (i assume, since JetBlue operates lots of them besides E-190s) could cost up to US$ 15,000 including the gas bottle for inflation. It took roughly 3 to 5 hours to repack them into proper working condition. It seems funny, but may pisses the mechanics off, and rescheduling flights due to unexpected delays like this could potentially have minor safety impact on the overall airport operations.
BTW, I like how JetBlue handle this one.