The way the multiplayer mode in GTA5 works is not very satisfying. Often you get ganked by some randoms and then go into Passive mode just to realize that even there you are not save.
Here is a list of some ways that people might kill a Passive mode person.

The thread which started it all: http://psteamcommunity.yuanyoumao.com/app/271590/discussions/0/617335934136545270/

1. • Grab a rocket launcher/Flare Gun
     
   • Shoot rocket/flare at the "Passive mode person"
     
   • Watch the flames beneath the hiding person burn him to death
   
   
2. • Grab a vehicle
     
   • Move/Push another vehicle with force into the "Passive mode person"
     
   • Watch the poor soul get crushed to death by the car
   
   
3. • Grab a Heli/Jet/Plane of your choice
     
   • Get some air with the Plane/Jet or speed with the Heli
     
   • Aim your movement towards the "Passive mode person"
     
   • Bail out just in time with your parachute and enjoy the explosion
   
   
4. • Find someone who is shopping
     
   • Get to the shop and shoot inside (preferably with police already being around)
     
   • Watch the person inside get shot to pieces

引用自 Nikomai Hurashi：

I killed a passive user by blowing up a car near them with a homing missile and they got irate.

引用自 peanut butter：

You also can start fires other ways, gas can, flare gun, rocket launcher what a waste of money...

You forgot shooting at NPC drivers and making them collide into the passive mode player.

引用自 Jay Dee：

1. Kill a few cops in a kuruma
2. Park next to him
3. ????
4. PROFIT!

引用自 GL Tricky：

1. Get in a car
2. Speed at him
3. Jump out before it hits him
4.????
5.Profit

引用自 Nordeland：

U can blow up him when he try to enter on plane, drive to him on kuruma and boom.