The initial idioms of the letter B

bestie	best-kept secret
best-laid plans go astray, the	best-laid plans of mice and men oft go astray
bestow on	bet a huckleberry to a persimmon
bet bottom dollar	bet dollars to doughnuts
bet (one's) boots	bet life
bet on	bet on it
bet on the wrong horse	bet one’s bottom dollar
bet someone dollars to doughnuts	bet the farm
bet the ranch	bet with
bet your bottom dollar	You betcha!
woe betide	betroth to
bet	betsy
better (oneself)	Better be an old man's darling than a young ma
better be going	Better be the head of a dog than the tail of a lio
better dead than red	better fish to fry