You say 'Boo!' loudly and suddenly when you want to surprise someone who does not know that you are there.
boos
A boo is a shout of 'Boo!' or another loud sound to indicate that you do not like a speaker or performer, their opinions, or their performance.
She was greeted with boos and hisses.
迎接她的是一片喝倒彩的嘘声。
boos , booing , booed
If you boo a speaker or performer, you shout 'boo' or make other loud sounds to indicate that you do not like them, their opinions, or their performance.
People were booing and throwing things at them.
人们发出嘘声,并朝他们扔东西。
Demonstrators booed and jeered him.
示威者发出嘘声嘲笑他。