mr./ms. lucky hands

a person (male or female) who solves things in a wrong or negligent way but somehow it works

(the term is used sarcastically, its not a compliment)

-how much score did you got in the exam? i got 30/100

-90/100

-HOW DID YOU DO THAT?

-i just picked and marked random answers in the whole test.

-oh, how impressive: mr./ms. lucky hands...