A bachelor you are as long as you're free, until you marry (or cohabit.) For some a lonely pathetic, for others a unbound epicurean. A free companion. (Bachelor is also a short (2 years) higher education.)

A serious commitment in a relationship changes the single, his life and priorities. Shared concerns, desires and obligations as pursuits hobbies and friendships crowding into the background. But before it's so far, there is still partied and danced.
For this purpose, in the Netherlands a bachelor party, in Belgium a bachelor evening is organized shortly before marriage by friends or family of the bride or groom. It is usually kept as secret as possible and surprising, and is intended to party free another one last time (?)and enjoy together and have fun. The birthday boy is there, unfortunately, sometimes some of the victims.
Sometimes the celebrated is hoisted in a conspicuous or ridiculous garment, and he / she is poked at it embarrassing or (supposed) ludicrous orders to perform.
To the minds of some egging on whether the steadfastness of those who are going to bound to be tested is sometimes a stripper hired.
Keep it funny, do not let anyone do things they later regret.
A party exclusively for men is also called a stag, men party or bucks party. The girls have a goats party.