Inverted: "Welcome to Tropey's Grocery Store, sir. What will it be?" "Well, I'd like... to buy a fireproof rocket, to plant bombs in the Sun, to collect huge rans— hey, wait, that's my evil plan!"
Bob: "Gentlemen! Hear me out as I read to you this vital announcement! Eggs, bread, milk... are the foodstuffs that might become very expensive in the coming months!"
The "shopping list" is actually Lord Badguy's secret evil plan, coded with a special cipher that looks like a shopping list.
After Lord Badguy readed the list out loud, other characters laugh at his foolishness, except the Smart Guy. He recognizes several ingredients for making an improvised bomb in that list.
Bob actually meant to give another announcement, but accidentally took his shopping list instead, and hastily ad-libbed something fitting.
The message encoded with Lord Badguy's shopping list cipher is... another shopping list.
Everything Lord Badguy says or writes down, ranging from memos to his subordinates to hour-length speeches before his armies, is expressed in the form of shopping lists, him being unable (or unwilling) to express himself in any other way. His minions have long since got used to this and are actually fairly competent at figuring out what their Lord actually means.
"On searching the suspect's home, we found 6 pounds of marijuana, half a pound of crack, an ounce of heroin, 500 micrograms of LSD... no, wait, this is my shopping list."
Zig Zagged: Lord Badguy reads his evil plan, which sounds like a shopping list.But it's actually a code... that when cracked reveals another shoping list. But the innocent sounding food items are required for his evil plan... but then Lord Badguy realizes he's reading the wrong shopping list.
Averted: The villain keeps his evil plan in a pile of very similar documents, but he never ends up confusing any of the documents with the plan.
Enforced: "We need to show that Lord Badguy is a Harmless Villain, let's have him mix up his evil plan with his grocery list"
Lampshaded: "Oh wait, that's my grocery list... Hah, how silly of me to do something like that again and again..."
Invoked: The villain's office worker underling, who manages all the documents, deliberately makes the evil plan and some random document appear exactly the same to humiliate the villain.
Exploited: The heroes listen in carefully every time Lord Badguy begins to read something out loud, hoping to learn of Lord Badguy's future nefarious shopping plans.
Defied: The villain explicitly checks what he's reading before he starts reading. And he keep a copy of his evil plan on the back of every shopping list, just in case he forgot the original evil plan document.
Discussed: "Mess in the workplace is not good for you, Lord Badguy. I don't think I have to remind you of the embarrassing incident last week where you accidentally read out your shopping list instead of the evil plan." "Shut up."
Conversed: "So, in one of the episodes, Lord Badguy comes in looking all pompous and says: 'Beware, Bob, for now you shall experience the terror of my plan! Eggs, breads, milk— pffthahahaha!"
Deconstructed: After Bob accidentally begins reading his shopping list when he's supposed to give an important lecture, he is laughed out of the room and mocked for years afterward, eventually giving him a phobia of shopping.
Reconstructed: After Bob accidentally begins reading his grocery list and everyone starts laughing, he finds his lecture under it. Now that everyone is laughing and feeling good, they're more willing to listen to him.