For me the most annoying thing is playing when I know I shouldn't play.
This includes:
-Playing when I'm tired
-Playing multiple sessions in one day
-Playing when I'm hungry
-Playing when I'm angry
-Playing when I'm under any influence
-Playing when i'm in a state of 'need' i.e. craving a big win
Whenever I'm out there grinding I enjoy the game so much, it's such a thrill to get to play a game of wits and be rewarded for mental sharpness. Poker is awesome for anyone who has a gaming background be it checkers, bridge, chess, or others
The challenge comes in when that high kicks in, the high of making a big hand, winning a big pot, or having a big session... which leads to craving... craving another big hand, win, session, another spike in the dopamine receptors and this is where it gets hard
Like in life, nothing in poker is really guaranteed, and so to go in with high expectations of a specific outcome often leads to forcing the action and then frustration. For this reason I think it's really important to go in with a clear mind, and with no expectation, but just an intention to play well and be grateful.
Even when I overlimp in with a hand I should fold, or defend my blind with a hand I shouldn't this frustrates me. Because, even though in my mind I know I'm really just craving some action, some opportunity, some engagement in the game, what I'm really doing is setting myself out for a bad situation because I wanted a rush.
So ya, for me when I play anything less than my best is what frustrates me the most. And from shifting my source of frustration from what's outside me to what's within me, everything becomes under my control. My mood, my state, my feelings.
Anything that happens outside me, that's just the game, that's poker, and after playing millions of hands no 'bad beat' is really painful anymore (still annoying but only for a minute because I can recall being on the other side and reset) it's just part of the game because we are never entitled the 100% of the pot we may feel we 'should be' when we get all in as a favorite