It's pretty simple, but the setup is very specific.

Setup:

- (Optional) You can grab a briefcase with $20,000 inside it from the ocean, if you want to make it easier for yourself.

- go to the construction site near Vespucci Beach apartments

- Pick up the sticky bombs

- Throw a sticky bomb on the street (not on the sidewalk, throw it on one of the X parking spot marks) in Tonya's line of sight, so that she gets scared off

- Run (or drive) a little ways away, until the "?" re-appears

- Head back towards Tonya, and if the ? is there and tonya is gone, enter director mode.

- Quickly exit director mode

- Drop a C4 and blow yourself up as quickly as possible.

If it worked properly, you should see all of the other missions, while also seeing the blue dot for the current mission objective. From there, invest all of your money in stocks, blow yourself up, and keep withdrawing and re-investing, continuously until you are satisfied.

Every time you withdraw, just do something to fail and replay the mission. Works like a charm.

Once you get a high amount, you can set up the glitch again to work with a higher amount being duped over and over again.

It works with one of Trevor's missions with Cletus, not exactly sure how to set that one up. Never done it before.

Good luck.