Bachelor Party (A.K.A. Bitch Is Coming)

Held for a bachelor shortly before he enters marriage, to make the most of his final opportunity to engage in activities a new partner might not approve of.

B.I.G. Party (A.K.A. Bitch Is Gone)

Held for a new bachelor shortly after he exits his relationship to make the most of his new opportunity to engage in activities his old partner would not approve of.

See Urban Dictionary definition - B.I.G &
B.I.G Party