louse up

To ruin, spoil, mess up, or bungle someone or something. A noun or pronoun can be used between "louse" and "up." Her sudden decision to quit in the middle of the project really loused us up. I am not letting your crummy attitude louse up my vacation—if you want to be grouch, you can go somewhere else and do it alone!

Inf. to ruin something; to mess someone or something up. You really loused me up! You got me in a real mess! Who loused up my scheme?

Spoil, ruin, bungle. For example, The bad weather loused up our plans, or Your change of mind really loused me up. This slangy expression originated in World War I, when infestation with lice was the common lot of soldiers in the trenches; its figurative use dates from the 1930s.

To ruin or botch, to blunder. Undoubtedly alluding to the unhappy condition of being “loused up,” that is, infested with lice, this slangy term dates from the first half of the 1900s. At first it was used as a transitive verb, as in John O’Hara’s Appointment in Samarra, “Lousing up your date.” A decade or two later it was also being used intransitively, as in “Don’t trust her with the reservations; she’s sure to louse up.”