1、But you think that I'm crazy to believe that I can protect myself from a vampire who's flipped the switch on his humanity.
但你认为我是疯了才会相信我能保护自己不受一个毫无人性的吸血鬼的侵害。

flip switch
触动开关

e.g: Anna flipped the switch that opened the front gate.
安娜触动了打开前门的开关。

2、And why should I let the fact that my boyfriend was turned into a hybrid put a damper on an otherwise fabulous day.
为什么要因为我男朋友变成了一个混血儿就毁了这美好的一天呢。

put a damper on something
扫兴；使不那么好

e.g: A couple of knee injuries put a damper on his football career.
几个膝盖上的伤使他的足球职业生涯不那么美好。

3、Hey. Are you checking up on me? Because I'm fine.
打来查岗吗？我很好。

check up on
检查

e.g: Don't worry; no one is going to check up on you.
别担心，没人来查你。

4、You're not going to get in my way. You hear me?
别来妨碍我。听到了吗？

get in the way
妨碍；阻碍

e.g: Your social life must not get in the way of your studies.
你的社会生活不能阻碍你的学习。

5、It's all right. Be jealous by all means.
没关系，你当然可以吃醋。

by all means
=of course 当然（可以做...）

e.g: ‘Can I bring Alan?’ 'By all means!'
“我能带走Alan吗？” “当然可以！”