dario:
What i'd like to know is if such things happen even in discos and pubs
In regular clubs you won't experience that for sure

Still we would recommend you to hide a fact you are foreigner, so if you call for a drink, just say something simple or show with your finger in the menu like you can't say it because there is too loud. Anyway if you go to such places, you are always under risk, not just because you are foreigner...
dario:
May you even write down a list of the "unsafe" districts of the city?
As deeper you go from the center, as less safe there is. Like in any other city probably.
The districts full of
gypsies are Kengarags (specially it's closest to the city part, so called "Maskavas" street, or "Maskachka") and Plavnieki. Plavnieki probably is currently one of the most dangerous districts. You will find a lot of drugs and criminals there

I would say, the dark district is also everything which is placed on the "left coast" of Daugava river. When you arrive to Riga by air, you are actually on the "left coast", when you cross the bridge, and if you are in the Old Riga or Central Station, you are on the "right coast". I would not recommend to stay for a long time on the right coast.
The Old Riga, however, is stitched with video cameras and the police, so it's quite safe place to walk. I think districts near Central Station,
Reval Hotel are also visited by foreigners at most, because they are quite safe.
If you have one day free, I would recommend to visit
Kuldiga... it's a small town located about 3 hours by bus from Riga, in the very deep country. It has a unique atmosphere which you will see nowhere in Latvia anymore. A lot of historical movies are filmed here. It's like you are getting into the 19th century - old houses, fresh air, museums and the widest waterfalls in Europe. It's very impressive and it's worth visiting if you come to relax your body by the safe method

In Riga... well, I would say you don't need to have a plan, just walk the town in any direction, and visit what you discover on the way

There is
nothing special...
And you have a lot of chances to meet the girl offline, because you are looking like a nice guy

Good luck!