What is Everybody And Their Mom?
1.
More than just everybody. Same as adding 1 to an infinite number. Noun, never plural, always singular.
I tried to buy tickets to the Motley Crue tour, but everybody and their mom was there.
2.
Used in place of "a lot of people"
Person 1: Did you see Jenny's "25 things" note?
Person 2: Yeah! Everybody and their mom is making one.
See 
Random Words:
1. 
A chick's vagina.
'I took a walk down Mary's love corridor last night'
See Justin.. 
1. 
it something a person uses to make fun of another person to show how stupid they are...
"Wow man,,, i asked this chick 1+1 and she..