After walking long distances, especially in warm enviroments, the penis will chafe on the denim.
After seeing a dirt valve one could call out to a friend to alert them of perving opportunities. Incinuating that the penis has twitched as it has been excited so quickly and unexpectedly.
Said with a high pitched voice in the right tone can lead to some comical behavour.
When repeated gives off a more important vibe. The more chafes often means the rating of the girl out of ten.
"Check that dirt out! Chafe Chafe Chafe!!"