This word can also be combined with the word minky (see Urban dictionary entry on this word), to form 'minky negombo', which is a more powerful insult than when negombo is used in its own right.
The word orginated in Sri Lanka, where Negmobo is the name of a coastal town, which is minky.
Negombo can be also used in the plural sense - negombos or negomboids.
"You are a total bunch of negombos/negomboids"
"This work is totally minky negomobo"