wrong bus u idiot!

Santa and Banta are walking home after a night on the piss. They--ve got no money to get a taxi and are staggering all over the place when they find themselves outside the bus depot.
Santa has a brainwave and says to Banta, Get in there and steal a bus so we can drive home and I--ll stay out here and look out for the police.
Banta breaks into the garage and is gone for twenty minutes while Santa is wondering what the hell he--s doing.
Eventually Santa sticks his head around the door and sees Banta running from bus to bus and looking very worried.
What the hell are you doing, get a move on!
To which Banta replies, I can--t find a number 25B anywhere.
whereupon Santa, holding his hands to his head in disbelief, shouts, You idiot, steal a number 27 and we--ll get off at the roundabout and walk the rest of the way!