The initial idioms of the letter B

be a [crisis etc.] in the making	be a [Londoner etc.] through and through
be a (something) in the making	be a (something) through and through
be a bundle of nerves	be a barrel of laughs
be a bed of nails	be no bed of roses
be a bit much	be (a bit) on the large side
be a blessing in disguise	be a bundle of laughs
be as busy as a bee	be a card-carrying member (of something)
be a fully paid-up member of	be a chapter of accidents
be a closed book	be one sandwich short of a picnic
be a credit to	be a dead loss
be a dead ringer for	be a different kettle of fish
be a dime a dozen	be a far cry from
be a fate worse than death	be a figment of (one's/the) imagination
be a figment of imagination	be a fine figure of a (man or woman)
be a fine figure of a man	be a force to be reckoned with