It's a variation on the A-I-U-E-O song. "Yu is for yukkuri. Yu..."
In a Dirty Pair fan comic, Kei was singing the following version: A is for Anus. A... I is for Impotence. I... U is for Unko (shit) U... E is for Eizu (AIDS) E... and then she got to O is for... (various rude possibilities) but Yuri knocked her off the stage before she could sing it.
Omanko? (mamumamu) Ochinchin? (penipeni) Onanii? (fapping) etc.
Shark Attack said: It's a variation on the A-I-U-E-O song. "Yu is for yukkuri. Yu..."
In a Dirty Pair fan comic, Kei was singing the following version: A is for Anus. A... I is for Impotence. I... U is for Unko (shit) U... E is for Eizu (AIDS) E... and then she got to O is for... (various rude possibilities) but Yuri knocked her off the stage before she could sing it.
Omanko? (mamumamu) Ochinchin? (penipeni) Onanii? (fapping) etc.
Probably the first one.
Both songs are parodies of "Do Re Mi" from The Sound of Music, which in Japanese goes,
DO wa do-na-tsu no DO (Do is the 'do' in donuts) RE wa re-mo-n no RE (Re is the 'le' in lemon)