In particular, as a general rule, they're not allowed to watch rated-R movies and many PG-13 movies are also off limits.
In the season 2 episode "Epidemiology", Troy attends a Halloween party dressed as the Power Loader from Aliens.
Not only are Jehovah's Witnesses forbidden from celebrating holidays, you might say Halloween is the one they're most forbidden from celebrating since it involves magic and the occult (also a JW no no).
Additionally, Alien is an extremely violent R-rated movie, of the type JW's are not allowed to watch.
In the season 1 episode "Modern Warfare" and then again in the season 2 episodes "A Fistfull of Paintballs" and "For A Few Paintballs More", Greendale holds a paintball tournament. A real Jehovah's Witness would be forced to leave the school premises since Jehovah's Witnesses are forbidden from participating in any form of violence, simulated or otherwise.
JW parents, for instance, often refuse to buy their children toys with guns.
On Community one of the study group members, Britta Perry, is an openly atheist character who Troy spends a lot of time with, and at one point was even romantically attracted to.
In the season 2 episode "Competitive Wine Tasting" Troy pretends to be a molestation victim in order to kiss Britta.
In the season 2 episode "Advanced Dungeons & Dragons" Troy joins the study group in trying to help cheer up Fat Neil by playing a game of "Dungeons & Dragons" with him.
Jehovah's Witnesses are not allowed to play D&D since the game involves the use of pretend occult magic, and Witnesses are strictly forbidden from becoming involved with or even pretending to become involved with anything using magic, spiritism, or otherworldly powers. Community's Dean Pelton is a flamboyantly gay character with an obsessive attraction to Jeff Winger.
Part of Troy's backstory is that he used to play High School football.
Most JW's forbid their children from participating in organized sports or for that matter any after school activities.