a feeling of shame or worry about something in your appearance, your behaviour, or your past, especially one that other people do not understand.

I think Melanie's got a bit of a hang-up about her lack of education. (often + about)

The English are notorious for their sexual hang-ups.

• be like a cat on a hot tin roof
• be like a child in a sweetshop
• be like a deer caught in the headlights
• be like a dog with two tails
• be like a fish out of water
• be like a kid in a candy store
• be like a rabbit caught in the headlights
• be like a red rag to a bull
• be like a spare prick at a wedding
• be like chalk and cheese
• be like Fort Knox
• be like looking for a needle in a haystack
• be like painting the Forth Bridge
• be like rearranging the deckchairs on the Titanic
• be like ships that pass in the night
• be like taking candy from a baby
• be like talking to a brick wall
• be like two peas in a pod
• be like watching grass grow
• be like watching paint dry
• be like water off a duck's back
• be living on another planet
• bells and whistles
• belly laugh
• be long for this world