Goin' Fishin'

A young man walking along a pier sees an old man with his shoes off, trousers rolled up, legs dangling in the water and fishing with an imaginary rod. Puzzled, the young man asks “What are you up to?”
The old man replies “Fishing for fannies.”
Laughing to himself, the young man decides to humour him. “Fishing for fannies eh? Sounds good. Can I have a go?”
“Of course,” said the old guy. “Have a seat.”
So the young man sits down, casts an imaginary rod and says “So how many fannies have you caught so far?”
The old guy looks at him and says “You’re the third this morning.”