Is there an idiom for people who boast too much?

Solution 1:

There are tons of them. There's a whole sub-genre based roughly off the phrase "all talk (and no substance)". These generally have the form "all X, no Y".

Others culled from synonyms on the wictionary link below include:

• All bark and no bite.
• All booster, no payload.
• All bubbles, no bath.
• All crown, no filling.
• All foam, no beer.
• All ham, no let. (For you fans of The Bard)
• All hammer, no nail.
• All icing, no cake.
• All lime and salt, no tequila.
• All mouth and no trousers. (A corruption of All mouth and trousers)
• All shot, no powder.
• All show, no go.
• All sizzle and no steak.
• All talk, no walk.
• All wax and no wick. (Alternatively All wick and no wax)

My personal favorite from cattle country here in the USA is to say that a person is all hat and no cattle.

As a note to outsiders, for some people wearing a cowboy hat has become something of a cultural statement. Thus many people wear them who, if confronted with an actual cow, would have no clue which end the "moo" comes out.

Solution 2:

I believe a good idiom that describes this situation is blowing your own trumpet.