pugh interjection \a strongly articulated p-sound sometimes trilled & sometimes with a vowel sound following; usually read as ˈpü\
Definition of pugh —used to express disgust or disdain
cf. a previous question: The word "pew" (P.U., etc.) and positive or neutral connotation
Many people, myself included, grew up thinking this might be spelled P.U. This is something kids in the United States used to say all the time as in "P.U., that smells awful!" It shows up that way in the Urban Dictionary.
According to this grammar blog the OED has the main listing under pew.
The Oxford English Dictionary says the exclamation has been spelled
many different ways since it first showed up in 1604: “pue,” “peuh,”
“peugh,” “pyoo,” and “pew.”
p.u. An exclamtion denoting the presence a vile or unpleasant odor.
"P.U.," either use deodorant or keep your arms down!
I knew that B.O. stood for body odor and I think I thought P.U. might stand for something, but didn't know what. Now, I wonder if it isn't related to pfui from German which got anglicized as phooey -- also an interjection.
Others may know whether this has anything to do with the cartoon character, Pepe Le Pew, a skunk. I have an association to this as well, but can't find any evidence. I think it mostly likely that the creators were making a pun on an existing expression and spelling it pew for what I found as pugh. This seems to be chiefly an oral expression that people spell in different ways.