The examine text "A big 'do about nothing" refers to the fact that a wig is a hairdo. It also refers to a Shakespearean comedy, Much Ado About Nothing.
Before, if you clicked on the "Angry" emote and switch headgear while the emote is going, the emote would still continue, enhanced, until the end. This glitch was fixed by Jagex on 1 September2010 in a hidden update.
A powdered wig looks a bit like a barrister wig.
The enhanced Angry emote, while wearing this item, can be interrupted by walking/running to another square. If you cancel the emote this way then try to do another emote soon after, the game will tell you "You're already doing an emote!".