What does a gay guy and an ambulance have in common?
They both get loaded from the rear and go...woo woo woo.
The Ambulance Comparison
Explanation
Explain Bear
Listen here, you smooth-brained human. It is a back-door joke. Ambulances take stretchers through the rear doors and sirens go 'woo woo'. If you cannot connect the dots between that and gay guys, you are probably the reason shampoo has instructions.