From Longman Dictionary of Contemporary Englishmuck something ↔ up phrasal verb informal1 British EnglishDO BADLY to do something badly, so that you fail to achieve something SYN mess up I really mucked up my driving test first time.2 SPOILto spoil something, especially an arrangement or plan SYN mess up The bad weather mucked up our plans for a picnic.3 British EnglishDIRTY to make something dirty SYN mess up Who’s mucked up the carpet in here? → muck→ See Verb table
Examples from the Corpus
muck up• Maybe I was just annoyed that his friend tagged on and mucked it up.• Sure, politicians mucked matters up.• If you did find her a place, she'd muck it all up somehow.• Barton stopped looking for Beda Fomm: if all this muck was coming up, the target must be down there. 