I'm a bit upset about this year's bonus.a bit of還是a bit?
a bit “一點點，有點”，= a little,修飾形容詞、副詞；也可以作賓語、表語。
eg.I'm a bit tired.我有點累。
I ate a bit.
但要注意：not a bit = not at all “毫不”
not a little = much 非常
eg.He is not a bit tired.他一點兒也不累。
He is not a little tired.他非常累。
a bit of = a little,放在名詞的前面，作定語。
eg.I have a bit of water.= I have a little water.
3.quite a bit 相當多