muck something ↔ up phrasal verb informal ( see also ↑ muck )
1 . British English to do something badly, so that you fail to achieve something SYN mess up :
I really mucked up my driving test first time.
2 . to spoil something, especially an arrangement or plan SYN mess up :
The bad weather mucked up our plans for a picnic.
3 . British English to make something dirty SYN mess up :
Who’s mucked up the carpet in here?