For pics that make you say "Wow, I never even considered the possibility of this being crossed over with that." Not a seiyuu joke or namesake, but where the artist clearly just threw two or more series together almost randomly. Especially effective when Japanese media are crossed with American.
Although it may elicit this response, one must truly consider if there is anything Touhou wouldn't be crossed with.
Bonus points if the two series have nothing in common.
Applies to parodies too.