Most of my jokes tend to revolve around stereotypes or other raunchy material many people might take offense to so I tend to save them for specific company.  There is one I can think of off-hand that is clean.

A bartender is working one night and sees a duck waddle in and jump up on a stool.  The bartender says “What’ll you have?”
The duck says, “I’d like some grapes.”
The bartender responds, “I don’t have any grapes.”
The duck jumps down and waddles out.
A little later, the bartender looks up and sees the duck sitting on a stool again.  So he again asks, “What’ll you have?”
The duck replies, “I’d like some grapes.”
The bartender shakes his head and says, “I already told you I don’t have any grapes.”
The duck jumps down and leaves again.
About a half hour later the duck waddles in and jumps up on a stool.  The bartender asks, “Now what?”
The duck says, “I’d like some grapes.”
At this point the bartender has had enough and says in a fierce tone, “Look you little shit, I already told you I don’t have any!  If you come in here asking for grapes again I’m gonna take a ball bat and nail your feet to the floor!”
The duck’s eyes pop and he quickly jumps down and waddles out the door.
Sure enough, not long after here comes this duck again, waddles in and jumps up on a stool.  The bartender sighs, walks over and asks, “All right.  What do you want now?”
The duck responds calmly, “I’d like some nails.”
The bartender stops for a second, scratches his chin and says, “I don’t have any nails.”
The duck smiles and says, “Then how about some grapes?”