[Winterous]

I laughed at them and let it go, as we weren't playing for money or anything, but it was pretty annoying. Especially after telling them for 15 minutes that their logic was warp spawned.

One of my friends used to be like this, it's frustrating to deal with.
Give them an example, their vehicle is next to a block of Impassable Terrain, and their exit point is blocked.
They ED, show them how they can't disembark into the Impassable Terrain.
Then switch to enemy models, show them that all possible ways of moving within 1" of an enemy model (assaulting, and special rules) specifically state that they are an exception to the rule, and that that 1" radius is Impassable Terrain.

If they deny it then, then they're cheating, plain and simple, and you should tell them that.