Scooter injuries are by far the most common reason for hospital trips for gringos on the island, possibly more than all the rest put together. In the past few years I have had one friend killed and two more seriously injured on scooters in Mexico. My brother had three crackups on scooters before he was not allowed to ride them any more by my mom (he's in his 50's and Mom is in her 80's
).
If you have experience on these machines, then maybe it would work for you, but most who rent them on Cozumel don't. Couple that with alcohol and you have the proverbial recipe for disaster. Traffic customs are different there, so cars may not do what you would expect, and with those tiny little wheels, a pile of sand on the road can send you flying.