Which monsters have pickpocket messages?
 

Is there some rule for this? I've been surprised by which mobs will call out a thief and which will simply turn around and maul their face off without word.

I can only think of sentient mobs calling my rogue out. Goblins, elfs, orcs, the obvious ones.

Which mobs have called you out that surprised you I am curious.

It's been about a year since I was playing borgnach and had that happen. But, let's just say I've also been surprised by an instance when a monster did NOT call the rogue out.

Wondering if this is a bug or working as intended, can't say much more at this point

Sounds like it's time for a test and a comprehensive list for the wiki.

think all humanoids

Only mobs with a moral center tend to call out such banditry.