Sarcasm is an adjusted stress reaction.

Also, just how many weapons of mass destruction did the Doctor take when he left Gallifrey? I have this mental image of him going through the arsenals, "Hmm, yes, a Hand of Omega, yes, yes -- DON'T TOUCH THAT, SUSAN! -- a device to control the walls between dimensions? Pah, what possible use could I have for it?" And so on.

*snickers*
Maybe he took everything he didn't think the Time Lords were responsible enough to have? Like, "I'll give you back the slingshot when I know you've learnt to respect others," to a small child.