If you're looking to prove your musical abilities quickly, check out Test your musical skills in 6 minutes!. As of today, the creator has added new features to compare yourself to others.
By way of disclosure, I suppose I'm quite happy with my 80.6% score. Despite the test's purpose, it doesn't seem to have much to do with tonedeafness, but rather with pitch memory. If you heard me sing you'd probably guess I'm a whole lot more than 20% tonedeaf.