Okay, here goes

1."The enemy within." episode. When the two Kirk's beam up, look closely at Kirk's shirt. It has no insignia!

2. "Court Martial" episode. Various uniform changes. Every time Kirk is in the commodore's office, he is wearing is green wraparound. But, in between one of the scenes, he goes to a bar. He is wearing his Yellow tunic. But another scene follows when he is in the commodore's office, wearing the green. He goes to the bar again. wearing yellow! Also, when Spock realizes the computer has changed, he and McCoy beam down to the starbase, wearing usual tunics. But on the Starbase they are wearing the special occasion outfits. Molecular mix-up, eh?