Flash Company & Celtaddict:

The comments about any word starting with "B.." being suitable for a swearword is only about 100 years too late:

MARGARET
How strange! Oh, Master! Master!--how shall I express the all-absorbing gratitude that--(about to throw herself at his feet).      

DESPARD
Now! (Warningly).   

MAR
Yes, I know, dear--it shan't occur again. (He is seated--she sits on the ground by him.) Shall I tell you one of poor Mad Margaret's odd thoughts? Well, then, when I am lying awake at night, and the pale moonlight streams through the latticed casement, strange fancies crowd upon my poor mad brain, and I sometimes think that if we could hit upon some word for you to use whenever I am about to relapse--some word that teems with hidden meaning--like "Basingstoke"--it might recall me to my saner self. For, after all, I am only Mad Margaret! Daft Meg! Poor Meg! He! he! he!   

DES
Poor child, she wanders! But soft--some one comes--Margaret--pray recollect yourself--Basingstoke, I beg! Margaret, if you don't Basingstoke at once, I shall be seriously angry.

MAR
(recovering herself). Basingstoke it is!


From Gilbert & Sullivan's Ruddigore (or The Witch's Curse)

Nigel