The AI for the bots in CS:Source is horrible, I don't know if they use the same AI for Half Life 2 or not.
Start a game against easy bots on CS:S and get into a fight with any opposing bot, during the firefight, hide round a corner/wall, and then come out again, the bot will instantly headshot you every single time you do this. (Exception: If a bot on your team starts firing on the opposing bot, it will switch targets and not headshot you.)
There's also an annoying "bot catchup mode" where the more kills you get without dying, the more likely you are to be one-shotted from half way across the map.