Honestly, in my opinion I think it varies with age. For example, teens will have more opportunity to bust each other since they are just discovering themselves; and, don’t they really consider consequences. Thus nut tapping is very common.
College age it gets a little harder; but, in today’s day and age, they are more open about kinks and sex. And hormones still drive their life.
Late 20’s and later, it becomes more difficult. This group (and others) help, to find a session; and, and maybe more. But it is just like any one trying to find a hookup.
As to what to say, I find honesty is the best. Be up front and just ask.