Barcelona is small enough to walk across in an afternoon, which means picking the right barri matters more than picking the right bar. The vibe shifts every six blocks. Get the neighborhood right and the night writes itself.
El Born for the romantic who hates trying too hard
El Born is the easy answer for a reason. The streets around Passeig del Born and Carrer dels Flassaders are narrow, lit warmly, and full of small places where you can hear each other. Start with vermut at Bormuth on Carrer del Rec, then drift toward Santa Maria del Mar and sit on the steps for ten minutes. If things are going well, walk down to El Xampanyet for cava and anchovies, accepting that you will stand and that the place will be loud. If things are going very well, finish at Paradiso, the speakeasy behind the pastrami fridge on Rera Palau. The trick with El Born is to keep moving. Three short stops beats one long dinner.
Gràcia for second-date energy on the first date
Gràcia feels like a village that the city forgot to absorb. The plaças (Virreina, del Sol, de la Vila) function as outdoor living rooms, and the move is to pick one and let the night settle around it. Plaça de la Virreina is the most date-friendly: the church wall, the orange trees, the kids running around until midnight. Bar Canigó on Plaça de la Revolució has been there for a hundred years and serves a vermut that costs less than a metro ticket. For dinner, La Pubilla near the Mercat de la Llibertat does proper Catalan cooking at lunch prices. Gràcia signals that you are not trying to impress, which is itself impressive.
Poble-sec for people who want to actually eat
Carrer de Blai is the tapas-on-toothpicks street, and yes it is touristy now, but the surrounding blocks are still where Barcelonins go when they want pintxos without performing. Quimet & Quimet on Carrer del Poeta Cabanyes is the obvious pilgrimage: standing room only, conservas stacked to the ceiling, the montaditos assembled in front of you. Go at 7pm on a weekday or you will not get in. After, walk up toward Montjuïc and the Mirador del Poble-sec for a view that does not require a cable car. Poble-sec works because it gives you something to talk about (the food) without forcing eye contact across a white tablecloth.
El Raval for the date that might get interesting
El Raval is the gamble. It is grittier than the postcards admit, and the upper half (around MACBA and Carrer de Joaquín Costa) is more interesting than the lower. Bar Marsella on Carrer de Sant Pau has been pouring absinthe since 1820 and looks every year of it. Granja M. Viader, also on Sant Pau, invented the chocolate drink Cacaolat and is open during the day if you want something gentler. The Raval rewards a date who is curious and punishes one who is precious. Read accordingly.
Barceloneta for the cliché that still works
Everyone tells you to avoid Barceloneta because of the tourists, and they are right about July. The rest of the year, walking along the Passeig Marítim at golden hour with a beer from a chiringuito is one of the better things this city does. Skip the seafood places on the main drag and walk inland two blocks to Can Maño on Carrer del Baluard for fried fish at honest prices. Then take the W Hotel elevator up to Eclipse on the 26th floor, order one drink (it will hurt), and pretend you are in a film. One drink is the move. Two drinks is a budget crisis.
How to actually choose
If your date is from Barcelona, pick Gràcia. They will be relieved. If they are visiting, pick El Born. If they like food more than scenery, Poble-sec. If they are interesting, Raval. If it is summer and you want to swim later, Barceloneta. The city does most of the work. Your job is to not over-plan it.