That always happens. And unfortunately for the ESTP type, it always is seemingly that it happens because an ESTP or an ESTJ wants to point out flaws in an unfinished arguement when I've just given them the premise and I'm about to answer their question.
When I start speaking in a group I'm unfamiliar with, I can't resist looking at everyone and realising their eyes are on me. It puts horrible pressure on me, so by the time I reach the punchline I'm as quiet as a mouse.
when talking in groups I am usually just shy and cant relate or just like to listen. I never have much to say and sometimes if I did have something to say someone already said it, or I just dont want to look dumb.