Green’s Dictionary of Slang

1. compliant, unwilling to make a fuss or cause trouble.

1743		J.E. Weekes ‘The Intrigues of Jove’ in A. Carpenter Verse in Eng. in 18C Ireland (1998) 296: The girl would have taken a guinea, / Ay marry, a whore’s not so nice.
1951		C. Stoker Thicker ’n Thieves 51: If the public official has been ‘nice’ to them and has insured them the continuous operation of their rackets, they’ll be nice to him on election day and will spend their money where it will do him the most good.
1980		(con. 1950s) M. Thelwell Harder They Come 127: Mek dem laugh, man. Dem t’ink say I nice.

2. (US campus) boring.

1987

Eble Campus Sl. Spring 6: nice – boring, staid.