Or when you go out of your way to get the assist on every single kill in your vicinity.
Things such as: Playing as Janna, an ally has just fought an enemy who is now burning to death from ignite. You shield your ally, not mitigating any damage or increasing any of his damage, but getting the assist.
Or playing as an AD carry, your team can easilly kill an enemy, so you throw one auto attack at the enemy before going back to whoever you were supposed to be fighting.
Or playing as Soraka and ulting your almost full health teammate to get an assist on their kill from across the map.
Who do you think is the best at getting them?
Jarvan is up there in the top 5 I'm sure. His flag gives assists on assists. If an ally has damaged an enemy then walks into the flag aura, if they get an assist on a kill you get one too.