Blink and you'll miss it in the beginning of "The Mourning After" (1x10), as Bo and Kenzi talk to Dyson about the mystery of the week. Kenzi cracks a wildly inappropriate joke and Bo turns a slightly "I'm your big sister and I'm annoyed at you" look on her before it quickly turns into "Okay, that was funny".
Dyson: Had to pry it from her hands post-mortem. She cracked the shaft with her muscle spasms.
Kenzi: Ha. Shaft.
Kenzi in Dyson's body in "Original Skin".
For that matter, the serial killer in Lauren's body is pretty hilarious too. Zoie Palmer looks like she's having a ball.
After Bo is given amnesia and runs away from Kenzi:
Kenzi: What if Bo hitched a ride out of town and is dancing in a topless bar, despite rival girls trying to bring her down?
"Fae don't believe in divorce for the first thousand years. What? Is it okay to expect people to actually give it a shot!"
Also: Ryan versus Kenzie.
Vex forcing The Morrigan to dance half-naked.
Vex being the only one who apparently notices the UST between Kenzie and Hale.
Vex: Okay, seriously, am I the only one who can see this!?
In general, anything that comes out of Kenzi's mouth.
"I'm human remember? We drive SUVs and we drop sewage into pretty lakes and we will burn this planet to the ground if it means one more cheeseburger". Mind you it's only compounded by the fact that she's holding a chainsaw at the time.
Kenzi: He left her at the alter. For our other sister.
Two minutes later, at "book club" (drinking and gossiping).
Suburbian Lady: I always say if it's getting hard then something's going wrong. Kenzi: I always say the opposite, something's wrong if it's getting soft, am I right? Ladies: [gales of laughter] Kenzi: [to Bo] I'm good at book club!