Regarding Barçelona: As a straight male, if you speak and understand conversational Spanish you should have no problem finding clubs to hang in. If you don't speak Castellano (spanish), or you just know a few words and phrases, you'll most likely end up hanging in the obvious "English Pubs" and tourist venues that cater to English speakers which have become more and more common in Barrí Gotic, El Borne, and near the marina. You'll still probably enjoy yourself, but you'll pay a lot more for the same beverage refreshments and food. There are a couple of dance clubs that can be hot for straight men, but they have time restrictions (straights from 10:00 to 1:00, gays from 1:00 until 7:00) or one night is gay night and another night is straight night. Mostly generic European techno pop. Nothing like hanging out with a bunch of loud Brits blowing chunks all over each other at 4:00 AM.
If you were gay, I could recommend quite a few venues (bars, dance clubs, saunas, restaurants, clothing stores) where it's much easier to socialize with limited ability to speak the local language.