If you're out with her again on a night out, and it's all gone well, ask her if she wants to come back to see the puppy you're looking after, that it's a cute little blonde one with massive eyes, and about this big (size it up with your hands). If she doesn't come, tell her she must be a heartless puppy hating sadist and walk off; Otherwise, she'll swoon at the fact you've got one at all and probably get way too excited.
Then when she's back, walk into the living room, gasp loudly and say "Shit, someone's stolen Thor!" or some equally God-like inappropraite name for a tiny little puppy. At that point she'll either laugh and you can grab her anyway, or - if she's nuts - will flip out, throw a tantrum and walk out complaining about your duplicity (this is highly unlikeyl!

).
Either way you're a winner! And just as proof, this got me the girl I'd been chasing for the last three weeks back home with me Saturday. It obviously rquires the whole cocky/funny style approach!