In NYC in the 80’s blacks would slash people on the subway for fun.
Saw a guy get his lips split open (4 lips!) with one whack.
In addition to the box cutter, the standard move was to carry a small emergency razor blade in the rubber of the sneaker, in case one got sent to Rikers.
Some guy also figured out how to smuggle crack in his sneaker and was actually smoking it in a holding cell.
Where there’s a will, there’s a way!
At least here in NJ we can carry Mace (in NYC it is illegal).