Maybe he was just out of toilet paper and was signalling the guy next door.

"Darn, out of paper.(knocks on stall wall) "Hey, bud!"

"Yeah?"

"Any extra TP over there?"

"Sorry, hardly enough for me."

"Any newspaper, candy wrappers..."

"Sorry, no."

(Reaches for wallet) "You got singles for a five?"

"You're under arrest."

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If they can get you asking the wrong questions, they don't have to worry about the answers.