I'm going to challenge this. Many of us here were not diagnosed until later in life and lived for many years before even the professionals could figure out we had bipolar disorder, so no, I don't think you can tell someone has bipolar disorder just be casual observation. In fact, even during the period of time when I was at my most severe, causing me to be hospitalized multiple multiple times, most people around me had absolutely no idea I was even ill because I am extremely good at carrying on on the outside when it is chaos on the inside.

Thus may be the case for the OP. I have no idea.