I could see this for Ps. I have heard that the main difference between IxTJs and ExTJs is the amount of energy they have to put into their work. I know a couple ESTJs that are very forceful and energetic in work and family matters, but get real "introverted" in non-work related social situations. They are definitely Es but have no interest in going out and partying.An extrovert with social anxiety would WANT to go out and interract with lots of people, have loads of friends and go to parties/bars etc, but would feel to scared to do so out of fear of rejection or appearing awkward or getting hurt, or just feeling held back by something. The lack of a busy social life would upset them.
An introvert would be perfectly happy with just having a couple close friends and going out occassionally =)
^This. It's all about the energy.I guess the main thing to look for would be that once they've gotten comfortable and have opened up to you, they would be energized from socializing and would want to keep going, as opposed to an introvert who would get tired after a while and need to withdraw and recharge.