It is a word said after you say something very sarcastic. It basically means whatever was said in the previous sentence means the opposite.

to turn someone on/make you horny

to send someone postcards, in particular those with notes about when you will see them next

A cigarette dipped in formaldehyde. Smoking a stick of woo causes the user to become very warm, creating a desire to strip away clothing.

A word used to express exicitement or celebration.

When you sit down for a wee, but then realise you need a poo.

Half of woohoo
Usually used to denote a slight bit of enjoyment, or accolade. Sometimes used sarcastically.