J'en peux plus - I can't take (it) any more. For a complete list of useful French phrases, get your copy of this essential French phrasebook. essential French Phrases and Expressions to Build Your Confidence in Speaking French.
I use this phrase a lot in English, so having it available in French is highly entertaining. I am the type of person to intersperse my English with Spanish, fragments of French, and the occasional word or two of German.