In prisons, abuse of a sexual nature, either in single instances or in a pattern of conduct, can present an Eighth Amendment violation, but courts should not constitutionalize every malevolent touch.
http://www2.ca3.uscourts.gov/opinarch/162939p.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.