Koper has a large student population, and there are plenty of bars around...if only I had been given a bed on the 20+ ward, and I might have been able to find out a bit more! As it was, I had to be content with watching the passeggiata through Titov trg down to the seafront...the loggia kavarna is a good place to watch it from, then head to the kavarnas by the market which are the places to be seen.
There is no nightlife in Koper! Move at least to Zusterna, that is only a rew minutes out of Koper, where you can find a place either if you are a old ricker or a young dancer! And you can find drinks there for reasonable prices.