"Sh*t the bed". Used when something particuarly unfortunate occurs.
Examples include, sh*tting the bed or even worse going home early after a night out in Liverpool, returning back to your unnamed hotel and soiling the carpet and walls (?) of a whole hotel corridor. Of course, to emphasise your stupidity, you will first take off the majority of your clothes, 'hide' them in a hotel cleaning cupboard for no apparent reason and alert the german workmen staying in the same hotel of the treat you've created outside their door by banging on it loudly shouting "2 world wars and 1 world cup".
You will of course complete the embrassing episode by losing your watch, wallet and mobile phone and then be "showered down" by one of the disgusted hotel bar staff (who will have found you unconscious).
Your first comment in the morning will thus be; "S.T.B".