"Can I borrow your knife"?
Hell no. If you don't carry a knife if your own, I don't trust you with mine. And by "knife", I don't mean a S&W or MTech. Heck, my boss carries a Microtech Makora 2, and judging by its condition and how sharp he (doesn't) keep it, I'm not sure I'd trust him using one of of mine. I wouldn't even trust most people with my Opinel. Yeah it's cheap and practically a throw-away, but the amount of time I spent getting it as sharp as it is - is not replaceable.
Oh, and by the way, I carry a Swiss Army Knife. If you want a screwdriver, I'll give you a screwdriver. My knife's tip is not a screwdriver.
"Why dou you need that knife"
As im cutting a package open for them!!!
Yep, that's a dumb one. Usually when someone asks me why I carry a knife I'm clearly using it to do knife stuff (opening a packaging, cutting a box, etc).
Then there's "why do you spend so much money on knives?"
Well gee, why do you spend so much money on sneakers/jewelry/watches/car stereos/tattoos/computers/Scotch whiskey/whatever? Because it's a hobby and it makes me happy.