A rat stash is a very thin and broken pathetic excuse for a mustache that certain individuals grow in a feeble attempt to look older while in reality it hinders ones appearance and makes them look dumber than they already do. People that possess them are usually 15 - 18 year old Caucasian kids that weigh under 140 lbs and act try to act like and dress like someone from a ghetto or low income neighborhood when in reality they grew up in a middle to upper middle class suburb (A.K.A. Wigger). Rat stash's can be found prominently in the South Philadelphia / Delaware County, PA area as well as their surrounding areas (New Jersey, Newark DE, Marcus Hook, etc).
Look at that punk ass wigger looking kid getting on the R2 to Marcus Hook! He has a rat stash!