You fool, to forget your birthday!
=You are really foolish to forget your birthday.
你真蠢居然把自己的生日都忘记了。
I was foolish enough to believe what Jeff told me.
我真蠢居然相信杰夫和我说的话。
You fool, to forget your birthday!
感觉这个句子不对吧,为什么用不定式,好像应该是祈使句才对,这个不定式符号 to 是多余的吧。