This command will disable combat AI for all NPCs in the game. When combat AI is disabled, NPCs are unable to engage in anything combat-related (so they won't be able to attack you). It is not possible to toggle combat for a specific NPC.
This is the only way this command can be executed. The above command would toggle combat artificial intelligence for everything in the game.
ToggleCombatAI is simply a longer version (alias) of the TCAI command - it has the exact same function.