It comes from the word manaf which we (in Bulgaria) sometimes use to name gipsies. So manafitsa is a bunch of people from the Gipsy minority crammed somewhere. Manafitsa actually came to me after thinking of banitsa and I saw a gipsy, so I combined the two words and there.. we have a new word :)
It's pronounced MAH-NA-FIT-SA :)
-Hey man, do you see all those black gipsies over there!
-Lol, man! They've become, like, a big manafitsa!