From the game EVNova, Drop bears are fabricated creatures used as an excuse to rip off
gullible tourists in the territory of the Auroran Faction. Drop bears are fabricated to drop from
high ceilings in spaceports and knock visitors unconscious; the visitors then come to in medical units with
high medical bills. The true identity of a drop bear is a thug who is on intimate terms with the medical staff and knows how to scam
people out of
money by knocking them unconscious. to further the scam, these thugs sell cans of 'drop-bear repellent' to anyone gullible enough to buy it; if someone buys it, then they are deemed gullible enough to later knock unconscious and pin the blame on the fabricated 'drop bear'.
offering to sell someone drop-bear repellent is a crative and highly round-about way of calling them gullible