Is 'ruffle' used correctly in this sentence?
The usual verb you are probably searching for is rattle.
Google ngram searches for ruffle our confidence, ruffled our confidence, and ruffled their confidence produce flatlines, while rattled their confidence is in obvious use.
This is reflected in raw Google searches.
- "ruffle our confidence": 9
- "ruffled our confidence": 3
- "ruffle their confidence": 3
- "rattle their confidence": 65 000
- "rattled our confidence": 37 000
This though the words 'rattle' and 'ruffle' are synonyms meaning fluster ... unnerve, when used with a person as DO. Only 'rattle' has apparently broadened to accept related DOs such as 'confidence', 'composure'. Probably 'rattle' is more drastic; 'shook their confidence' is, according to raw Google data, far more idiomatic.