There's no use getting mad about the snake poo on your bed. Have you tried taking it somewhere with newspaper? Maybe it gets nervous when it's first out in the open, and poos, and if it could poo somewhere safe first, then it wouldn't poo again and you could put it on your bed?
Snakes just poo. Usually poo more when nervous, but it's not a "I'll show you!" type of thing. Annoying yes. If you don't ever want poo on the bed, I'd say the only sure way to not have the snake poo on the bed is to not put the snake on the bed at all.
Wolfy