With our stroppy 18 (almost 19) year old, it's the threat of not being able to have her boyfriend stay the night that usually does the trick.
Otherwise, their internet (which they all heavily rely on) is individually cut off. Hubby (Cowasaki) set up a big lockable box in our bedroom, which looks like a telephone exchange with lots of cables going in and out. All their rooms are individually networked, so the plugs are pulled at the first sign of attitude and being spoken to like you're something they just trod in. The main computers downstairs are also rendered out of bounds.
We don't exist as people in our own rights, we don't know anything, we've never done anything, they invented fun, sex, etc, etc - we're just there to make their lives run as smoothly as possible, and woe betide their cushy little numbers don't go so smoothly sometimes - it's always our fault!
GGGGGGRRRRRRRRRRRRR back atcha!
From mum of four (almost 23, almost 19, 17 and 15). Oh and the 22 year old is just as bad, even though he's moved out and has a baby of his own! He still expects me to pick up the pieces when things go wrong and still talks to me like he's trodden in doodoo and I'm the doodoo!