There is a very easy way of doing this at the start, no working up to it required.
Anyways, start a new game, choose the Landgraab household that is in the south east corner, these sims already have a bunch of friends.
Set up a fundraising party at the Rendezvous Cove (beach that is left to their house), make dressing swimwear.
Simply attend the party, have your sims set to free will, so all you have to do is watch, at the end of the party you will get the achievement.
This worked for me, it should work for some others.
Also, do not change the time, otherwise this will "glitch" you out of the achievement first time.