I'm a horrible offender of all three types of frustrating kills whenever I play as a sniper in A.V.A.
Sometimes those three categories overlap - a one-hit headshot kill system really puts quite an element of luck into gameplay, as people get random unintended headshots quite often, especially if the spread of a gun is quite high. I really hate headshot systems, except maybe when sniping (I dislike one-hit snipers if it doesn't require a headshot to kill in one hit, but I'm fine with one-hit sniper headshots).
When both players in a Quake III duel have a lot of health and armor, the kills don't fall into any of those three categories. There are no headshots, and none of the weapons have any recoil (only the machinegun and the shotgun have any inaccuracy at all), so you can't blame randomness for anything except maybe getting an inconvenient spawn location. The game gets a lot more frustrating if you start getting repeatedly spawn-killed, though, since there are a lot of one or two-hit kills that you really can't do anything about.