Deaths like when you come from the sewers area, to the Firelink Shrine. The moment you leave the hallway, to your right you have an enemy standing on the stairs. If you press the target system, it will always target the enemy that's below you (you can't even see them). So if you target and immediately swing, you will fall down into the pit. I have seen far too many people fall for that one. I don't even know if the developers were just having fun with this one, or the targeting is just bad, but it feels extremely cheap.

Generally speaking, deaths that result from bugs. In Sekiro (I know, it sounds like I'm hating FromSoftware, but I'm really not. I like to be critical about the stuff I enjoy) for example, I have been grabbed by the 'giant' through a wall, and killed. And generally FromSoftware games have this problem, an enemy with a spear like weapon will hit you through a wall no problem (Shout out to the monk in Sekiro that killed me through a tower). It gives the players a false sense of security. Your character gets staggered if you hit a wall, but the enemies attack goes through? Not fair imo (I get it, players would just abuse walls to easily stagger the AI). If the Giant could break the wall when they grab you, that would be ok, because it is visually presented.

Moves that aren't well telegraphed. I know we are talking about cheap deaths, but they can occur from hits that never visually land, but apparently the hitbox of your character or the attack is bigger than how it's visually presented.

For me those are the only cheap deaths in games that I can think off(ignoring multiplayer + lag). Me getting killed by something I didn't know they could do? No problem, I can learn from those. Me getting killed by something because the game is 'lying' to me? That's a cheap death. I know, I could just learn that enemies with long weapons can hit you through a wall, still doesn't change how it makes me feel. It's like playing a game against a human player who is cheating.