I dunno. It depends on the work environment. If it's one of those "we're all basically peers but one guy happens to be the manager" type of teams then I don't see it as being that outrageous.
Being told you have to go to a Strip Club, and that sort of environment is something that makes you uncomfortable (male or female), then that is sexual harassment.
Defending it just because most of you are 'mates' in/out of the workplace is not acceptable.
It's tough. I used to have to go to strip clubs with managers and customers. Required attendance. It gets weird after a few trips.