The "Fun with barrels" easter egg was discovered after Gearbox developers started posting hints, by user 'SenorGuacamole' on the Gearbox Forums. If you pause while the rider of the "fish" is in view, it seems to be Patricia Tannis. This was confirmed by SCole on the Gearbox Forums.
- Go to the secret dock in the south east, where you get the "You're on a boat!" achievement.
- Shoot the yellow barrel to the right of the dock.
- Shoot the green barrel in the distant trash pile east of the boat.
- Shoot any of the blue barrels on the boat.
- Shoot the red barrel in the water to the left of the boat.
- Enjoy, and start tripping.
The music that plays when Tannis appears is 'Snifty's Loading' by Raison Varner (Gearbox audio lead). It was originally going to be 'Nemo's Jam', also by Raison, a song which still appears on the game disc.