It's not like he could pick one weirdest thing about his life, and even if he could, this wouldn't be it. Foreknowledge of the apocalypse would definitely beat it out, or the first time he rode behind a killer's eyes, and the whole sex thing, well.
So this is just a weird little thing, almost innocuous: the visions leave unexpected echoes sometimes. He's never smoked a day in his life--he was a biology teacher, for God's sake, he showed that blackened lung to hundreds of kids before he became a car accident statistic--but now every time he smells a lit match, he gets the craving, remembers the way it felt, the way a cigarette fit between his fingers, between his lips, the sweet (foul) taste of smoke, the (choking) way it filled his lungs. He wants it, and he knows exactly why he never wants it. Every time somebody strikes a match he remembers, and gets a little closer to buying a pack out of sheer borrowed need.
"Johnny?"
He snaps back, looks up at Walt on the other side of the barely-kindled campfire. The smoke is rising thin and white between them, but Walt's eyes are dark and steady. Johnny just shakes his head and looks away. It's almost innocuous, the way he remembers being unable to live without things he never wanted. Almost.