不眠之夜 white night　
不明飞行物 unidentified flying object (UFO)
不拿原则换人情 refrain from seeking personal favor at the expense of principle
补缺选举 by-election
不惹是非 Stay out of trouble.; Let sleeping dogs lie.
不速之客 gate-crasher
不惜一切代价 spare no effort; go all out; do one's best
不信任投票 vote of non-confidence
步行街 pedestrian street
步行天桥 pedestrian overpass
不夜城 "sleepless city, ever-bright city"
不以物喜，不以己悲 not pleased by external gains, not saddened by personnal losses
不遗余力 spare no effort; go all out; do one's best
部长级会议 ministerial meeting
不正当竞争 unfair competition
不正当竞选 illicit competition
不正之风 bad (harmful) practice; unhealthy tendency
步兵师 infantry division
不倒翁 tumbler; never-fall doll
不扩散核武器条约 Treaty on the Non-Proliferation of Nuclear Weapons; NPT