Dick on horseback

On Christmas morning a cop on horseback is sitting at a traffic light,and next to him is Johnnie on his shiny new bike.
The cop says to Johnnie,"Nice bike you got there.Did Santa bring that to you?"
Johnnie says ,"yeah."
The cop says,"Well,next year tell Santa to put a tail light on that bike."
The cop then proceeds to issue Johnnie with a $20.00 bicycle safety violation ticket.
Johnnie takes the ticket but before he rides off says,"By the way thats a nice horse you got there .Did Santa bring that to you?"
Humouring Johnnie,the cop says, "Yeah,he sure did."
Johnnie says ,"Well, next year tell Santa to put the dick underneath the horse,instead of on top."