The initial idioms of the letter B

be a rough trot	be a sight for sore eyes
be a sign of the times	be a sure thing
be a thing of the past	be a thorn in flesh
be a thorn in (someone's) side	be a (something) to (one's) fingertips
be a hard act to follow	be a waste of space
be a weight off (one's) shoulders	be a weight off shoulders
be about	be above board
be absorbed by (something)	be afraid of (one's) (own) shadow
be afraid of own shadow	be after
be after blood	be out for/after (someone's) scalp
be after (one's) blood	be against
be ahead	be ahead of the game
be ahead of the pack	be alive with
be all	be all (the) one (to someone)
be at sea	be all beer and skittles