An interview is a very artificial social situation which makes it especially difficult to read people, because they don't act how they normally would.
It's pretty common for interviewers to come across as overly stern or critical, as a result of taking that role of evaluating someone else. Many interviewerspeople don't even realise they're doing it, or at least not the extent to which they are. They're often projecting an impression back at you which is nothing at all like the one they actually have.
The point being, just remember that you really have no clue what someone else on the other side of the interview table is thinking. You really don't. Certainly never act on it!
Even in the very rare case an interview is going badly yet they have to continue because of process or law, it's not a waste of time at all, it's a great opportunity for a learning experience - a real interview situation where you've nothing to lose and can practice your interviewing technique, perhaps even trying some new things and taking some risks. And hey, you never know, you might even turn it around by doing this!