The Sims 3
50 Achievements
1,000
30-35h
It's a Date
Went on a date.
20
How to unlock the It's a Date achievement in The Sims 3 - Definitive Guide
Select the husband or wife, go to the bistro on the town map, select 'eat here with others' then choose your husband/wife from the list and they'll both go together.
You get the achievement as they leave the bistro I think.
Once you get to at least a love interest relationship status with another sim you can ask them to go out on a date. Use your sims' cell phone to call out your new love interest and click invite out. From there you can invite the sim anywhere you want. You can take them to the park or to a movie or anywhere else as long as you take someone out. To actually go on the date you must interact with the area where you took the sim out. For example if you take him/her out to dinner you're going to have to eat at the restaurant with your date, simply meeting them there isn't enough. This trophy will unlock when the date is complete.
First of all you will need to get your relationship with another Sim to "Romantic Interest" status. After you have done that go onto the "Town Map" and select a location such as the cinema or a restaurant and select the "go with.." option. Then choose the Sim you want to go on a date with and when it is over this will unlock.
This is made a lot easier if you start the game with a male and female Sim.