A comical, somewhat discrete and "polite" way to say my niggahs.
The pronunciation of manigas is easy to pronounce. Instead of saying My Ni-ggahs, one says Ma-neegas spoken faster than usual to achieve that pronunciation (sound) of a military general saying "Manigas! Get me the President of the United States!
Often used to call one of your close friends without meaning any harm.
It is typically used as a replacement word for actual names/subjects/items/etc. Originated in the University of California, Irvine when a group of undergrad students in the fields of biology and engineering became extremely high.