In the buff and Without a stitch

In the buff adjective - (used informally) completely unclothed.

Without a stitch and in the buff are semantically related in without covering topic. In some cases you can use "Without a stitch" instead an adjective phrase "In the buff", when it comes to topics like without clothing.

Without a stitch adjective - Without any clothing at all.

In the buff and without a stitch are semantically related in without covering topic. You can use "In the buff" instead an adjective phrase "Without a stitch", if it concerns topics such as without clothing.