Green’s Dictionary of Slang

shyst adj.

[backform. f. shysty adj. (2)]

(UK black/teen) aggressive, promiscuous.

[UK]Skinnyman ‘Love’s Gone from the Streets’ 🎵 Nowadays even the girls are shyst.
[US]Tennessean (Nashville, TN) 7 Aug. 25/5: ‘That guy, he’s so shyst’.