"Beauty is in the eye of the beholder" means "different people have different opinions about what or who is beautiful". Example: It’s true that beauty is in the eye of the beholder. I haven’t found any of Mary’s boyfriends attractive.
“Let your hair down” means “to relax and do what you want”. Example: It’s been such a hard week at work. Should we all go out tonight and let our hair down a bit? Origin: This phrase originated in the century, when women were expected to wear.
“My ears are burning” means that you know or think that other people are talking about you. Example: I can’t believe I fell over on the stage last night! My ears are burning now – I’m sure everyone is talking about me. Origin: This idiom originates.