too big for one's britches

too big for one's britches idiom
Also, too big for one's boots. Conceited, self-important, as in Ever since he won that tournament he's gotten too big for his britches, or There's no talking to Jill anymore—she's just too big for her boots. This metaphoric idiom alludes to becoming so “swollen” with conceit that one's pants or boots no longer fit. [Late 1800s]

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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