[sitter] See: [ON THE FENCE] also [FENCE-SITTER].

[sitting on a powder keg] See: [SIT ON A VOLCANO].

[sitting on top of the world] See: [ON TOP OF THE […]

[sitting pretty] {adj.}, {slang} To be in a lucky position. * […]

[six] See: [AT SIXES AND SEVENS], [DEEP-SIX].

[six bits] {n.}, {slang} Seventy-five cents. * /"Lend me six bits […]

[six of one and half-a-dozen of the other] {n. phr.} Two […]

[size] See: [CUT DOWN TO SIZE], [PINT-SIZE].

[size up] {v.}, {informal} To decide what one thinks about (something); […]

[skanky] {adj.} Dirty, particularly of a marijuana pipe.