Are smartasses born or bred?

Really, I wonder.  Some kids are very literal for a very long time and some, well, not so much.  William seems to get it.  He's not literal.  We joke and kid and play (Kid 'N Play!) all his joyous moments throughout the day and it's a ball.  He has great facial expressions and uses his hands like an old Italian man.  I wonder how he became this way, though.  We joke and have fun and make light of stressful situations (like having to go back upstairs to get your sweatshirt or something tragic like that) so I know some of his disposition has obviously been learned.  I just wonder if you are who you are who you are.  You know? 

Tonight the four of us were playing in Drew's room before bathtime while Lauren was already asleep.  William yelled.  I told him not to, reminding him that Lauren was asleep in her room down the hall.  He yelled again.  I told him very sternly that I would spank his bare bottom if he did it again.  *this is where I must say, just in case you don't really know my parenting all that well, that I absolutely do not tolerate disprespect or rude behavior in any way, shape, or form *  William said with enthusiasm, facial expressions, and hand gestures, "If you spank me, I will kick you.  And believe me, I'm an awesome kickah."  He laughed just as hard as Chris did.  Where the hell did that come from?  He has never kicked me nor has he ever threatened to, I can assure you.  He knew the response was inapporpriate yet funny yet he was in a safe enough place to say it.  

Soooo, at the tender age of  3 years, 4 months - has this been learned or is this just who he is?  And this comment is just the tip of the iceberg with him.  Trust me.