sometimes a group may charter a ship and if they cannot sell all of the cabins within 30-45 days there may be a clause in the contract that allows the cruise line to sell to the general public on a last minute cabin sale and if the cruise line doesn't advise the general public about who the majority group onboard, it could cause some interesting situations..
this actually happen to me several years ago and it turned out to be alot of fun for me (it was open up for interline bookings only)
my parents always taught me about being careful for what you ask for..for those posters that insisted who they "won't cruise with" or "would not want to be on a cruise with alot of_____ (you can fill in the blanks). they just might find theirself in that situation one day and I don't think trip insurance covers "personal biases or preferences"
smart cruisers know you don't cruise Disney if you don't like being around alot of small children, you don't take a 85 day world cruise if you want an active party night life etc