"Wasted Talent"
Season 2, Episode 20

Lois discovers that Peter has the piano-playing skills of Mozart...when he's hammered. But even if you're falling-over drunk, a proper tuxedo will fix your appearance right up (see: James Bond). Even though Peter can barely distinguish between the keys, he plays well enough to bring win first place at the local recital competition for Lois. Does it matter that only one of his brain cells is left intact when he looks so sharp?