One of my buddies splits his time between his business in Dallas and his place (I should say compound!) in Cozumel. I was able to meet up with him for a day on my last cruise there. He took me to some great local watering holes (NOT the tourist traps). I highly recommend these:
Kelley's Sports Bar & Grill (Bostonian ex-pat owns it)
http://www.islacozumel.net/food/kelleys/
El Fish, it's a cantina - FREE food/appetizers and CHEAP beer, like $1!!
no website, I think it's at the corner of calle 8 and avenida 10
Here's some info to help describe it, copied from (http://www.tripadvisor.com/ShowTopic-g150809-i66-k1846700-Are_there_any_Gentlemens_Clubs_in_Cozumel-Cozumel_Yucatan_Peninsula.html)"
"AND someone should have mentioned that the cantinas usually are closed by around 5-6pm (they open at around noon). The food is free with each round of drinks and you get many plates of finger food with each new round. There is no "ordering". Depending on the cantina, you can eat pretty darn well.....they usually start small and work up to better and better food even whole fried fish!! BUT beware that the BEST food is often gone by the later hours and once they are out of something, that's it. Also since the beers are cheap and the food is free, make sure you leave a really good tip-----even the poorest locals who frequent the cantinas for their afternoon meal leave 20%.
Two other good ones are El Fish on the corner of calle 8 and avenida 10 (one of my favorites--no entertainment)......and Miguelitos which is on the calle that is across the street from the old Ace Hardware on 30th....changed management recently but it used to have live dancers and music---it's a giant hall and used to be PACKED every afternoon....."