The "Plot Hole": Why didn't Jack and Rose just share the door? Even if they couldn't get on it together, they could take turns, right?
Why It Actually Isn't: First off, they did try to share the door, but it couldn't hold them both. And you can throw that Mythbusters explanation out of the window, because a scientific experiment conducted under perfect conditions is not applicable to the reality of two panicked people freezing their gonads off.
Then there's the fact that they both would've exerted unnecessary energy getting on and off the door in order to swap, which could very well have resulted in neither of them surviving. Rose wasn't exactly far away from death's door when she was rescued, after all.
And of course, you can't forget the chivalry of the day: of course Jack was going to be the one taking the icy dip, because he's a guy and it was 1912.
You might not love the decision making if you have zero empathy for two people caught in a horrendous situation, but it's not a plot hole in any sense.
Got anymore frequently mentioned plot holes that actually aren't? Shout them out in the comments!