不太
bú tài
Expressing "not very" with "bu tai"
不太 is the polite hedge — literally "not too", used the way English says "not really".
不太 + Adj. / Verb
How it works
不太高兴 is "not very happy", 不太喜欢 is "don't really like it". It softens a negative judgement, which is why it turns up constantly in polite conversation.
Note that it is 不太, not 太不. It works with verbs of feeling and preference as well as adjectives.
Examples
tā bú tài gāo xìng
他不太高兴。
He isn't very happy.
wǒ bú tài xǐ huan zhè ge
我不太喜欢这个。
I don't really like this one.
jīn tiān bú tài rè
今天不太热。
It isn't too hot today.