What do you do if people deliberately take kills away from you?

You say gj and press to take the undefended tower.

KS = kill secure

If the jungler is coming into my lane and the enemy is at 50 hp, I want the jungler to take the last hit. 450g > 300g

There's no such thing as kill stealing. That's only a low ELO mindset. Now ideally if the jungler is ganking bottom they should let the ADC grab the kill if it's secure even if the ADC did no damage to deserve it, but securing the kill is much more important than that.

Goal of the game is for 5 people to beat 5 other people, since a kill is about the same as 20 minions, why sweat it?

I dont really care, in the end it is more gold for the team

Spam my emotes, and laugh. I don't mind when people try super hard to take my kills, and when it involves a pointless flash it brings me joy.