# louse up

CEFR B2 · Phrasal verb

Source: https://englishreference.com/word/louse-up
Updated: 2026-10-22

## Definition

to spoil or ruin something by making a mistake or doing a bad job.

For teachers: to spoil, ruin, or bungle a situation or task. Transitive; typically implies a lack of competence or care leading to failure.

## Examples

- I hope I don't louse up my job interview today.
- The project was going well until a small mistake in the budget managed to louse up the entire plan.
- Despite months of meticulous preparation, a single logistical oversight threatened to louse up the diplomatic summit's opening ceremony.

## Pitfalls

- Not "Don't louse up it." but "Don't louse it up." — when the object is a pronoun, it must go between the verb and the particle.

## Usage notes

- this verb is separable, meaning you can put the object between 'louse' and 'up'.
- Teaching tip: contrast with 'mess up' or 'screw up'; 'louse up' is slightly more old-fashioned but still common in informal American English.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.