Is relativity common knowledge?

[Aerozord]

Sometimes things I consider basic I find out isn't well known to people in general.

Yesterday I got into a heated debate with someone about long distance space travel. Two specific things of course came up. First was that as an object approaches the speed of light it takes more energy to accelerate it. Which is because of the second point that mass is energy, which also brought up that there is a set amount of energy within our solar system. Both of which are covered under general relativity.

I seemed to be the only one that knew about that. The reason the debate broke down is because I was trying to give a little physics lesson so they can understand why faster than light travel isn't possible but you know how people get when you do that. Plus the argument devolved into the tired old assumption that we'll just find a way to break the laws of physics because ... science.

Anyways I was just curious was this a fluke or do most people not know of this layer of physics?