What does it mean when someone says you're full of malarkey?

When someone says you're full of malarkey, it means they think you are talking nonsense, lying, exaggerating, or saying foolish things that are not true, but said in a relatively mild, humorous, and non-vulgar way. Malarkey is American slang that means nonsense, bunk, baloney, or hogwash, so the phrase is equivalent to saying you're full of nonsense or you're full of it, but without using profanity like bullshit. It is used to dismiss someone's claims, excuses, or stories as untrue or silly. For example, if someone makes a wild excuse for being late, you might say you're full of malarkey, meaning I don't believe you. The tone is usually scolding but playful, not extremely hostile, and is considered acceptable in polite company, media, and politics. The phrase became famous as a catchphrase of President Joe Biden who often says you're full of malarkey to push back on false statements. The origin of malarkey dates to 1920s American slang, believed to come from Irish surname Mullarkey associated with tall tales. So when someone says you're full of malarkey, they are calling you out for dishonesty or foolish talk in a colorful, old-fashioned way that means you are not being truthful or serious and should stop the nonsense and be honest.