Leave a sour taste in one’s mouth = to leave a bad feeling or memory with someone.( a negative impression).

• The way they conducted the interview left a sour taste in my mouth.  I don’t think I’d accept the job even if they offered it.
• I know Jim is your friend, but he was so rude at dinner; it just left a sour taste in my mouth.
• The way the waitress treated us left a sour taste in my mouth and I never went back.

To the bitter end = to the final, most critical extremity such as death or total defeat.

• My father stayed beside my dying mother’s bed to the bitter end.
• The worker would fight to the bitter end.

Bear fruit = yield positive results.

• Eventually her efforts bore fruit and she got the job she wanted.
• Our apple tree didn’t bear fruit this year.
• Don is convinced that this plan will bear fruit if we just keep working on it.