Another term for Irish Knacker, nack, scumbag, scobe. Wahs congregate at street corners or in Arthurs Quay park. Native to Limerick City, wahs wear tracksuits, often carry knives ("My friend Stanley"), and cause general disruption at any given oppourtunity.
Watch the get-up of that scobey wah, with his friend stanley.
Further to earlier explanations, within the British Army, also used in response to an answer to an obvious question. This is a question that you have set the other person up to answer. Can become quite frustrating as you become paranoid answering any question in case it is a Wah!
Steve "Is that a can of beer in your hand Bill?"
Bill "Bugger, been Wah'd again!"