A time traveler walks into a bar

A time traveler walks into a bar. He sits down and order a drink.
The bartender sighs and slowly pours him a glass.
The time traveler asks "What's the matter?"
The bartender says "I've been a bartender for 30 years today. I've seen people come and go and I've heard literally every 'person walks into a bar' joke. Every one. 'Blonde walks into a bar' 'Neil Armstrong walks into a bar' 'An orange haired man and a duck walk into a bar'... I just can't be surprised anymore"
The time traveler ponders for a moment "You couldn't have heard all of them. New jokes are being made every day".
The bartender shakes his head "I'll prove it. What do *you* do?"
The time traveler says "I'm a time traveler. I cross the streams of times and fix paradoxes"
The bartender smiles and says "A time traveler walks into a bar... A time... Traveler walks into a bar... You know, I've never heard a time traveler walks into a bar joke"
The time traveler replies "I don't think I did either"
The bartender sighs again "Look, I gotta go back to my customers. Enjoy your beer"

The time traveler sits and thinks, he makes it his mission to brighten the poor bartender's day with a "time traveler walks into a bar" joke.
He sits on the stool for hours, trying to come up with something until finally an idea strikes him, the most perfect "time traveler walks into a bar" joke ever thought of.
He looks around the bar for the poor bartender but can't see him. He asks the man behind the counter. He said that bartender's shift was over and he's gone for the day.

The time traveler decided to go back a few hours and cheer up the bartender with his joke. He got into his time machine, twiddled the knobs and went back in time.

In front of him is a massive wasteland and untamed land. A cliff with several caves is nearby. The time traveler checks his machinery "Damn. I overshot it. It's the right date and time, but the wrong year". A neanderthal gets out of his cave and approaches the time traveler. He grunts at the time traveler "You look strange. Who you?"
The time traveler says "Me? I'm a time traveler. I was supposed to meet a friend of mine here, but... Hey, want to hear a great joke? A time traveler walks into a bar-"
The neanderthal holds his hands up and stops him "Too soon! Too soon!"