The two reactions I get are:"Hey, that's pretty neat, I guess a swiss army knife CAN do everything"Or"That's way too small, how am I supposed to write with that thing"When I get the latter I just replace the pen and slowly deploy the blade. Then I ask for their finger. When they ask why I explain so I can cut it so they can write in their blood. When they ask if I'm crazy I say "nope, but seeing as you don't have a damn pen of your own and mine isn't good enough for you, that's your only option"
My wife usually rolls here eyes.