The polar bear represents Bundy Rum, and is in all their ads.
The "drop bear" term resembles these three guys on a camping site trying to pick up these three Swedish backpackers, with the guys warning them about Australian wildlife in the bush, which includes "drop bears", which is just like a koala bear, but only bigger. Anyway, the polar bear is sitting up in the tree, then falls down, right where the girls are meant to camp. It's a plan to get the girls to camp with the guys, that works.
So there you go.