Nickname #4 is “Sweet Cheeks” (Season 1 Pilot Part Two) directed at the spunky and spoiled Shannon Rutherford. 
Seeing that it is Sawyer, he was probably making a snarky comment about her backside. But there is a chance that he could have been referring to her youthfulness.
< Kate made mention of her concern that Shannon might be a little on the “young” side for such a treacherous trek up “Hollywood & Vines” Mountain. Shannon swiftly quelled Kate’s fears in her signature demure manner with the reply “What are you, two years older than me? Please!”
