Yeah, Silverstar, I like your suggestion of Luke just turning away and heading to his hut. That would have at least prolonged the intrigue that was carried over from TFA, while not being such a complete dismissal of both the saber and the audience anticipation. He also could have taken the saber and returned it to Rey.
If the point was to use the lightsaber hand-off that was set up in TFA as a way to convey Luke's dark/lost state of mind, it could have still been done in plenty of ways without a letdown that was the consequence of choosing to go for levity. If Rian Johnson wanted to go dark, he could have had Luke look at the saber for a while, then turn his attention to Rey with a menacing look. Luke could ask Rey something like, "Do you know what happened to the man who first held this lightsaber? He turned on those who were looking to him as their hope for salvation. He slaughtered many of them with this very same weapon." Luke then ignites the saber, slowly approaching Rey with a dark and sinister expression, and asks Rey, "Tell me . . . What were you hoping to find here? Your hope for salvation?" Then, as Rey backs away in fear, Luke draws the blade down and hands the saber back to her. He tells her that she wasted her time chasing him down in hopes that he'd come save the galaxy. And that would have kept Luke in the same state of mind that Rian Johnson wanted, but by using the conclusion of the lightsaber hand-off to build drama and intrigue instead of go for a cheap laugh or a "gotcha" moment.
If Rian Johnson didn't want to go as dark, he could have had Luke talk about how when he first held that saber, he was filled with awe and wonder, and convinced of the delusion that he could take his father's saber and fulfill his father's destiny to free the galaxy from the clutches of evil. But now (Luke could explain as he thinks out loud), the nightmares he'd seen (and helped create) have destroyed the young dreamer that he once was. He could have tossed the saber at that point, or given it back to Rey, and been clear that he wanted no more to do with the fight to take down the Dark Side.
There are dozens of ways the scene could have played out that simultaneously respected the mystery established in TFA and kept the same story of demoralized TLJ Luke intact. Instead, we got to have a few people in the theater laugh or chuckle a little. Yay.