Here is how the National Football League explains rule on taunting:
Taunting of an opponent is a foul under N.F.L. playing rules and will be called by the game officials (15-yard penalty). In addition, the taunting player will be fined.
Any flagrant acts or remarks that deride, mock, bait or embarrass an opponent are considered taunting. This includes, but is not limited to, spiking the football near a defender after a touchdown, shoving the ball at an opponent, or repeated finger-pointing. Remember, if you spike the ball near an opponent after a play, you risk being called for taunting even if you don't mean to taunt.
Player demonstrations (for example, end-zone dances) are not fouls under N.F.L. playing rules and will not result in penalties by the game officials. However, if a demonstration constitutes taunting (see section immediately above), or if it is unsportsmanlike conduct or delays the game, a foul will be called.