When not doing errands or in my house, I am occasionally seen:
-Eating by myself in restaurants because I can't be bothered to get a group of people together, but I really want to try the food there.
-At art museums, by myself, because I can't be bothered to find a group of people who are interested/available/not going to run around screaming.
-At small concerts, with someone else, but never in a large group.
-At the library, reading in a corner.
Many NTs are easily identified by one of the following: an angry-looking concentration face, a clear lack of understanding of the aesthetics involved in dressing yourself, a huge pile of books obscuring their faces, generally looking nerdy, or ruminating on the merits of post-colonial literature/physics/philosophy etc etc
ENTPs and ENTJs are impossible to distinguish from ESTPs and ESTJs in chaotic social settings, apart from their bizarre sense of humor and the fact that they are clearly taking notes and coming up with plans for world domination (hint: you can see this in their eyes).