no russian

An expression you use at videogames when you kill too many players/npcs in a row, most of the time being all of them unarmed. If the players/npcs are in a group the phrase will be more fit.

It originated thanks to Call of Duty: Modern Warfare 2, game that has a mission where you go to an airport along with Makarov and his men to kill innocent people (citizens), and this happens too fast ending up in a lot of corpses and stuff I better save for myself (Spoilers).

Man, I was playing as citizen along with my boys at Half-Life 2 RP when a defunct CP came and did a no russian on us.

Me and my brother found a village at Minecraft, I was looting the chests when I hear he does a no russian on all villagers, this boy is really crazy and stupid.

lowkilling

In gaming, lowkilling is when a player kills other player that has low health points, mainly because of a previous fight or doing revenge on that player.
This is considered one of the most coward or bad ways of killing another player, and is commonly done by noobs, people who wait the ending of fights to kill the remaining player(s), or by players who get defeated at a fight or 1v1 and seek for revenge.

Player1 killed Player 2 with sword.

Player1: You left me with 9 hp, I don't know how I survived this haha.

Player3 sees the aftermath of fight and realizes Player1 is low and attacks him.

Player3 killed Player1 with knife.

Player3: Damn, that was too ez bro.

Player1: Shut up man, I had low hp that was lowkilling.

Player2: Yeah don't be a dick and accept you did that man.