1 Moto/ATV Off-Road Race
1 Water Race
1 Flight School Lesson
1 challenge on 1 gun at the Gun Range.
Finish 1st on Franklin's Shift Work's Strangers & Freaks sidemission. This sidequest only shows up between 22:00 pm and 05:00 am if you're a little into the story.
No need to get Gold on all, example, Triathlons, just 1 is enough :)
You don't need Tennis, Golf, Darts and stuff.