The fallacy of questionable equivalence (or in some cases, false equivalence) occurs when an arguer regards two things as being similar, but overlooks a significant dissimilarity that undermines the intended use of the comparison.

Here is an example:

Glen: "Sorry that I can't come to the reunion -- I broke my tibia skiing."

Wes: "Oh, I tripped and sprained my ankle last Summer, so I'm familiar with what you're going through."

Wes is drawing a false equivalence. Although both accidents involve an injury to part of the leg, a broken tibia is much more severe and has different consequences than a sprained ankle does -- so Wes is not "familiar" with what Glen is going through.