The fallacy of relative privation or 'Appeal to Worse Problems' is a fallacy in which one dismisses an opponent's argument because the problem that they are trying to solve is not the worst problem.
"Gun control? But cars kill more people than guns, and you aren't trying to get rid of those."
"Obama might be detaining people without trial and bombing civilians, but Bush did far worse."
This is closely akin to a false dilemma, tu quoque, or appeal to tradition, and generally the fallacy of relative privation can be reduced to some other fallacy. Even the canonical example -- "eat your vegetables, there are starving children in Africa" -- is a form of non sequitur.
It should be noted that there are cases where arguments of this form may not be fallacious. For example, "I'm not going to wash the dishes right now, because the house is on fire" is perfectly sound reasoning. To show that an argument is committing this fallacy, you must show that the order of solving them does not matter, or, alternatively, show that one problem cannot be solved (e.g., Bush having been president), and therefore need not be considered.