A man was standing at the bar drinking when a Vietnamese guy walked up behind him, yelled, "Aaaaah-ha" and hit him across the back of the neck, knocking him out cold.
"When he wakes up, tell him I know Kung Fu!" the Vietnamese man said to the bartender, then he left.
A while later, having come around and given the mysterious message, the bloke was just about to order his drink to numb the pain in his head when another cry of "Ahhhhh-Ha" rang out. Once more the man hit the floor after being decked from behind, and once again the assailant gave the bartender the same message before vanishing.
Half an hour later the Vietnamese man reappeared. Looking around, he asked where the man had gone and was told that he had staggered away, looking sort of green around the gills.
The Vietnamese man shrugged, ordered a beer and was just about to take a sip when a loud "Ahhhh-Ha" sounded behind him. In an instant he was flat on the floor, out like a light.
"When he comes to, "The bloke said to the barman, "Tell him I know crowbar, mitre10, $9.95!"