The most fundamental flaw is that while something like this may be amusing if it was a real life challenge, in comic form, we all know that Randy just thought up some song title combinations. If he couldn't think of a good combination for lesbian voyeurism, he would have come up with something else for Girl to say, after being prompted by some other challenge from Guy. These things are funny when they happen in real life precisely because they are improvised, and so seeing it in comic form will never be funny, no matter how clever it is.
But that is not the only problem! We have the glaringly stilted exposition of "SO I HEAR YOU CAN COMBINE SONG TITLES TO MEET ANY CRAZY DEMAND, EH?" first line. Might as well start The Hound of the Baskervilles with "SO YOU'RE SCARED OF A BIG OLD DOG THAT'S ON YOUR PROPERTY?" it just thrusts the reader into this horribly contrived scenario that doesn't make any sense or have any resemblance to real life - and the terribly awkward phrasing of that sentence is an effect of this.
Obviously this comic fits all the usual xkcd problems of creepy (take normal songs and make them lesbian for me! and have me WATCHING.) but on the second one, hell, it's not even lesbian. You don't know what gender the narrator is. Sure the girl is female, but then any love song to a girl would become lesbian. You only have one and a half examples, here, randy!
Look: We all know what happened. You thought of this one only mildly amusing mash-up and constructed a comic to use it as a punchline. And forced yourself to think of a second title, and failed to make it fit the category. Good job! you do not understand comics.
In other news, hey! Randall posted something funny on his blog! ha ha, but it was just because it was a quote from Joey Comeau.
heads up by the way that next week i will be off to Mysterious Lands yet again, and everyone's best friend Commenter Jay will be taking over posting. I don't think he's posted yet so play nice everyone.