Wiktionary
sloucher
n. A person who slouches.
WordNet
sloucher
n. a person who slouches; someone with a drooping carriage
Usage examples of "sloucher".
Warren, something of a sloucher himself, regarded this spectacular slouch by the limp long brown bulging-eyed trombonist with incredulity.
Here on paper was just the young featherweight sloucher she had first seen, Plopped against a red Siena wall in the noon sun.