This phrase is often employed when one accidentally touches someone inappropriately, say while brushing against a coworkers bosom while squeezing past in a crowded elevator, and is used to convey that the inappropriate touch was unintentional.
One should take care that this phrase is not mistaken for "No, Cuomo," which roughly translates to "Please pardon my predatory and inappropriate behavior, for I am of Italian descent and don't know any better."
"I meant to reach for the cellphone in my back pocket but accidentally touched Jim's crotch, so I said 'no cuomo' to let him know it was an accident."