In Are You My Mummy?, the girls are given a super-powered shovel for one of their missions. The minute Clover turns it on it spins out of control and out into the desert. Turns into a Brick Joke when the shovel actually comes back during the fight with the Big Bad, and Clover actually greets it with "hello, old friend!" After the shovel's done its duty, Clover lets it go free again, saying "be free, old friend!"
And from the same episode, Alex's "Easter Bunny" dialogue when the girls are briefed, which is too funny to spoil. The other girls' reactions also settle it.
From "The Fugitives", part of Sam's disguise falls off when they investigate the bank that their evil look-alikes robbed, leading to a guard telling her "Uh, sir, you forgot your… mustache?!"