The bee's knees. Or rather, the knees of the bees xD
I've always laughed at that idiom, not that my native language has less weird idioms
Sometimes i don't give a damn about making mistakes while speaking English, because i see, though we have taken too much grammar lessons during the education, in daily life most of the native speakers don't care about such details.
When i first graduated, i used to speak English as if i was reading the sentences from a grammar book. And it used to be really weird, so i gave up being so careful.
Sometimes i translate English idioms into my language, idioms and slangs such as 'scare the crap out of smb' make people laugh hard.