It's rather lame dialogue -- Auron's enigmatic, but this exchange is pretty random even for him! His second quote's a good one though.
(This is for all the folks who, like me, have the habit of talking to Lulu all the time so that we never get to see any of the alternative ones.)
The delightfully scathing game synopsis on videogamrecaps.com pointed out by nancy2004 has figured out what Auron was up to here:
Speaking of our favorite guardian, he rides his snowmobile next to Tightass, pondering whether or not he should run Tightass off the nearby cliff. Tightass whines, "You're no fun to ride with at all." Auron doesn't give two shits what Tightass thinks, and tells him, "Just don't do anything rash." Tightass, unsurprisingly, is confused. "I'm saying you should not complicate matters. [sez Auron] Or you'll find yourself trapped, understand?" "I don't need you to tell me that!" Tightass wanks, as if he even has half a clue what Auron is talking about. A little while later, Tightass admits that Auron makes sense. "Make mistakes," Auron replies. "That's what youth is for after all. Do not waste it." "So which is it!?" Tightass whines. I laugh when I realize that Auron is just fucking with Tightass's head.