目の上のたんこぶ（めの うえの たんこぶ） is a serious hindrance.

「目の上のたんこぶ」（めの うえのたんこぶ）is used for a person who makes it more difficult for you to do something that you want to do. It is especially used for your superior.

「たんこぶ」is a slang for 「こぶ」, which is a bump or a swelling.

You can also say 「目の上のこぶ」（めの うえの こぶ）.