[fma]

You can't stand in the front, due to security concerns with being near the cockpit. Back is fair game. More common on international flights, though. Plus international flights they have snacks in the back, so you can stand there and munch.

[hkmurakami]

Great to know (knew about the snacks but was never sure if I was allowed to loiter). Thank you!

[Smaug123]

Remember, if you loiter politely while in flight, the worst anyone official will do to you is ask you to go back to your seat :) very little downside to trying even if it's "not allowed".