The initial idioms of the letter B

be (living) on another planet	be (not) (one's) bag
be (not) (one's) brother's keeper	be (not) a patch on
be (not) a pretty sight	be (not) all beer and skittles
be (not) all fun and games	be (not) all moonlight and roses
be (not) as black as (someone/something) is painte	be (not) backward in coming forward
be (not) big on (something)	be (not) comme il faut
be (not) on speaking terms	be (not) out of the woods
be (of) no use to man or beast	be (one's/the) main squeeze
be (one's) for the asking	be (one's) pigeon
be (out) on the piss	be (out) on the razzle
be (really) something	be (right) on the money
be (sitting) in the catbird seat	be (sitting) on (one's) tail
be (sitting) on top of the world	be (someone's) call
be (the) bomb	be (the) devil's advocate
be (walking) on thin ice	be a [athlete etc.] in the making