I can't say it was the weirdest, I probably don't remember the weirdest one, but I do remember one that was pretty weird. It was years ago, too, but I still recall it as if it was yesterday.
I dreamt that I was on Mars, in an armoured rover, an all-terrain kind of vehicle with like 4 or 5 other astronauts. We were cruising along some Martian plain, looking to recover some satellite that crashed nearby. Suddenly, an elderly African man dressed in all white (and with no spacesuit on, too) stopped our rover and tried to tell us some cryptic warnings through the window (which could be lowered like a car window, because it's a dream and it doesn't have to follow engineering conventions...). We kinda laughed it off (but didn't question his existence at all) and continued onward with our mission. We could already see the crater where the satellite crashed and were almost there.
Then, everything started shaking, and the ground began to break up and rise, like during an earthquake (or rather, marsquake?). I was lucky and got thrown out of the rover somehow through the still-lowered window, as the vehicle fell down into the abyss to be crushed by shifting rocks.
I found myself on a huge tilted slab of... well, the ground. Everything was still shaking, and a huge volcano arose in the distance. And that's the weirdest part - three enormous... snake heads came out of the volcano on long serpentine necks and started devouring the world around them. I realized, somehow, that this absurd spectacle was the end of the world, and I envied my colleagues who were likely already dead. So I started walking away from the volcano, only to eventually arrive at a Martian beach on the coast of a Martian sea - the beach was made out of the same red sand, with rocky outcrops stretching into the water. There were dozens of people there, just chilling in swimwear and waiting for the end.
I sat on the beach with my helmet off, when I saw a gigantic three-headed serpent similar to the first one rise up from the water on the horizon and start to slurp the ocean up. That's when I woke up.