Here are some fun options for dealing with someone who has told you the same thing several times, as if it is the first time:

1) “That story gets better and better every time you tell it.” (This option is not nearly as fun/entertaining as the following two).

2) Turn it into a fun conversation, by retaliating…I mean responding…with questions demonstrating interest, but slightly off from what was stated. For example, using your falling-off-the-bycycle-in-junior-high-skinning-knee-neighbors-laughing example — consider interspersing the following questions in the follow-up discussion.
a) “You rode a motorcycle in junior high?” or “Why were riding a tricycle in junior high?”
b) “Why did your cousins laugh at you?
c) “So who won the bike race?”

As the conversation progresses, lots of othe opportunities to ask inane questions will present themselves.

3) This last option has proven to be very, very effective in dealing with the behavior. Look for every opportunity over the next several hours/days from the latest re-storytelling to pre-emptively bring up the tired story. For example:
a) “I vaguely recall that you fell off your bike once.”
b) “This episode of vintage 90210 reminds of the time when a friend or acquaintance…can’t remember exactly…fell off their bike and were embarrassed for some reason. Do you remember what I’m thinking of?”
c) “I think you should use the treadmill rather than the stationary bike. Didn’t you have an incident last summer or something with a bike. I can’t recall the details.”

Again, opportunities throughout the day will create neat and creative ways to bring the topic up.