It happened in a checkout line a few weeks back. The latest serious climate change warnings had just come out, emphasizing glacial melt affecting sea levels, and the right wing had already jumped in with its blind denials. Their bad analogy was an interesting one. The discussion was an agreement between the checkout lady and her 7-ish customer, and being next in line, I shamelessly eavesdropped.
He was spouting nonsense about ice cubes melting in a glass, claiming the water level wouldn't rise a bit once the ice melted, further citing that "fact" as proof that melting glaciers would have no effect on sea levels.
There were just two things wrong with his argument. First, the glaciers in question are currently mostly sitting high and dry above the sea, not floating on it. They will melt, move down, and add to the total liquid water in the oceans. The amount of total ocean water will change.
Second, he apparently has never actually watched ice melt in a glass. Try it. Add ice cubes to water so that they are just floating, not standing on the bottom. Make a mark on the glass for the water level. Notice that some amount of the ice sits above that water level. Let it melt and check out the water level again. Yep, it will be higher.
Those ice cubes represent the floating glaciers. Only 1/8 of them actually sits above the water level. Still, 1/8 of them does sit above water level, and when they melt, will raise that level too, same as the land glaciers will. The amount of water does not change, just the amount of liquid water.
Ain't a little bit of actual science grand?
Of course, the two deniers holding forth in front of me were not likely to be dissuaded by anything resembling facts or observations. I didn't figure it worth my time to step in and start that argument. I wanted to get through the line myself before my ice cream melted. Its frozen condition wasn't as long-lasting as any glacier, and I prefer the taste/texture in its original condition.