Use the adjective lanky to describe someone who’s tall, thin, and a little bit gawky.
A lanky person is not only tall and thin but also a little bit awkward. You wouldn’t use lanky to describe a tall, slender person who moves gracefully. Instead use lanky to describe someone who moves clumsily on his long limbs. You’ve probably seen a lanky basketball player who moves awkwardly but is still able to make the play, or a lanky teenager who seems to be made up entirely of long legs and long arms.