the irrational fear that you will be unable to access a restroom because of extenuating circumstances, such as a full pew at church or a long line at a bar
Pewp is a more intense version of poop, with the change in spelling meant to suggest violence (i.e. "Pew-pew-pew!", as if feces is being launched from, rather than squeezed out of, the anus.)
A picture or "selfie" taken of someone who clearly hasn't showered or brushed their teeth in several days. Basically, you can smell them through the picture.