I asked about the jokes here and, according to Nhi Lee:
Also the Tang clan is often joked about broken legs because their flying skill is very hard, newbie and oldie often fall and die, hence the joke lol. As a Tang class's member I can confirm this, if you haven't fall while flying and "broke your leg at least once a day" you cannot call yourself a Tang clan lol.
Also, Tang Clan is said to be crazy about DPS so they are also often joked about wooden dummy being their lover (something to test your dps on).