Alter-ego - a separate account set up on an online forum different from your regular username so that you can discuss something you don't want attributed to your normal account.
Attention Whore; this does not always have a negative connotation as you'll often see posts on TheKnot where someone "AW's" their wedding or something they made, etc.
Bridesmaid (or can be Best Man, depending on context)
By The Way
Short for Chapel of the Flowers wedding chapel in Las Vegas - http://www.vegasgroom.com/Chapel-of-The-Flowers_24.html
Double Decker Bus - this is specific to the Vegas section of TK, it's a bus company who rents, wait for it, double decker busses like you'd see in the UK, enclosed downstairs, open top. They're a popular transportation option between ceremonies and receptions to buy some time and go on a photo tour.
Day Of Coordinator
Future Father In Law
Fiance or Fiancee depending on context
Future Mother In Law
For What It's Worth
Good Bye Cruel Knot - Leaving the knot forums, typically not planning on returning.
Hope That Helps
In My Opinion
In Real Life
Mother Of the Bride
Maid of Honor
Made Up Drama; frequently used when a new poster posts something ridiculous or calls someone out, because typically it's really a regular using a phony account just to start drama.
No Further Text
Not My Style
Not Wedding Related
Oldie But Goodie