So in addition to all that other dick joke crap, which I've written about before but not as thoroughly as I plan to soon, there are some serious problems.
Now I don't know how many of you understand the context here, which is an old joke that is told more or less well on this forum post. We know that the comic is referring to the joke, because if you don't know about the joke, the logical conclusion is that he asked for a "miniature pianist" and then received a "miniature penis" which would in theory replace the current one. That of course would make the final line, from the woman, very confusing indeed.
So we know that the point of this comic is to refer to the old "Twelve Inch Pianist" joke. And the problem that that leads to is the same one we had with the horrible Bill-Watterson-would-be-rolling-in-his-grave-except-that-he's-still-alive comic from last week: All it does is refer to the previous funny thing (assuming you think the piano joke is funny) without adding anything new at all to it. What's the point? That he went the other direction, asking for a pianist and getting a penis not the other way around? That's not the point of the Old Joke. That's basically just a pun - "pianist" sounds like "penis." The end. What's the joke here? Same thing. Worse though, because it's not original and isn't even pretending.
Also: Using the shot in panel two for scale, assuming a vaguely normal sized human head, that grand piano is maybe 6 to 8 inches long, and the person playing it would be maybe 2 or 3 inches long, tops. So if he asked for anything larger than 2-3 inches, the little fellow would not be able to play the piano, and if he were 2-3 inches or less that girl at the end would not be so impressed. This actually bothers me almost as much as that other stuff.
Anyway, there are so many things wrong with this comic in so many very different ways. It sucks in all sorts of interesting ways.