Full of Hot Air: Origin and Meaning
Some believe that the phrase originated in the USA and was first used by Mark Twain in 1873. Others believe it to be used by Rudyard Kipling in the 19th century. This slang term has its origins in the United States, and it appears to date to the late 1800s. In addition to being “full” of it, something can be referred to simply as “hot air,” a shorthand reference to the longer saying. As a general rule, when one is accused of this, it is not a compliment.
– You’re so full of hot air. I don’t believe you.