How's about this:
Suppose you jump up with speed X, and forward with speed Y (combined into a diagonal move, of course). Now, either speed X is large enough to escape earth's gravity, or it is not. If it is, you're going to die for lack of oxygen; if it is not, you will eventually fall down. Given that your horizontal speed Y is finite, you will have a limit on how far you can jump.
...unless you escape earth's gravity field, in which case you're dead (as stated previously). In that case, good for you, and goodbye.
