Alternate title: Do you want to make 100,000 Bells in 10 minutes?
One of my friends told me about this, and at first I didn't fucking believe it because of how ridiculous it sounds.
So first off, if you haven't unlocked Tortimer's island go do that. After you build your house he will ask you to meet him at the docks, and if you do the next day Kapp'n will be there and will take you to the island for 1,000 Bells. Now there's a lot of neat shit to do on the island, but who fucking cares because we're here to get paid. Go to the island after 11 PM, talk to the gyroid outside to get a net, and then be amazed as you catch dozens of fucking beetles worth anywhere from 8,000 to 12,000 Bells all night long with absolutely no repercussions.
If you don't fuck up scare away all the beetles there's nothing stopping you from making 300k+ in one trip, it's really that dumb. I can't complain though, because it's allowed me to upgrade my house and build new public works so who gives a shit. I'm having FUN.
If you are not well versed in the fine art of beetle capturing here is an instructional video.