So so hard to do irl I find though.
Yes, acting classily and maintaining an aura of imperviousness can be difficult when you are at your most vulnerable having just lost a big pot. This is especially true when faced with unpleasant behaviour directed towards you, such as asking to see your losing hand or slowrolling you. The easiest way to achieve this is to genuinely not be bothered about such things. But
pretending not to give a fuck is at least a first step on the road to actually not giving a fuck.
I am not perfect in this stuff either, and here is a story to illustrate my own weakness...
A few years ago I was playing in a £2/5 No Limit game. I was having a torrid losing session, at the end of a torrid losing week, at the end of a torrid losing month. And then I was dealt AA.
I won't bore you with all the action... suffice to say quite a lot of money went in the pot preflop, plenty more went into the pot on a 224 flop and then I jammed a Jack turn for £800. My opponent was a guy called Ken - an experienced recreational player, who was quite aware of the etiquette of the game. He thought for a little while, then asked me how much it was. I told him it was £800. He then asked the dealer for an exact count. The dealer counted it down and confirmed it was £800. Ken thought for another ten seconds, then started to slowly count out the £800 chips to call. It took him ages since he counted it all out in £5 chips. Finally he pushed his chips over the line, with a look of resignation on his face. I insta-tabled my AA before the river was dealt, since it was obviously winning at that moment. He nodded and tapped the table gently with a sad little look on his face. The river bricked off and he just sat there shaking his head. He looked back at his cards as if about to muck them - then slowly, one card at a time... turned over two Jacks for the nut full house.
In that instant I resolved not to say a word, nor to even acknowledge the vindictive slowroll that he had just inflicted on me. Every player on the table was looking at me, watching for my reaction - demanding a reaction in fact. They knew what had occurred, as did he. And I just ignored it completely, reloaded my stack, and refused to be seen to acknowledge what had happened. I folded the next two hands, then quietly left the table to go for a smoke. When I was having a smoke break I calmed myself down and resolved that I would go back in, not mention it, and not give off even the smallest clue that it had got to me in any way at all. So I sat back down, put a smile on my face, and just got on with it.
But the thing is... it
had got to me. I was really pissed off with this guy, who was a regular player and definitely knew better. I felt attacked by him, and indeed I had been. So inside I was stewing a little bit, even if I was able to prevent any sign of this from coming out. It is actually a very empowering feeling to be able to give off an aura of "I don't care in the slightest" even when you do care. And I am proud to say that I managed to maintain this illusion...
... for about twenty minutes, at any rate.
Finally it got too much for me. I just couldn't help myself. I wasn't nasty or aggressive, and in fact all I said was something like, "Ken, what was with that big dwell on the turn in that hand before? Did you think I had quads or something?" No more than that. But that was all it took for me to lose, and for him - in a sense - to win.
When you are slowrolled, or needled like the OP was, you are placed in a situation in which almost any response you make will result in you losing. This means that the only response you can make is to give no response. Which is, in fact, the most powerful response of all.
Do this for long enough, and eventually you learn to really not give a fuck.