Final answer:
Gilderoy Lockhart attempted to use the 'spell' Peskipiksi Pesternomi in 'Harry Potter and the Chamber of Secrets' during a Defence Against the Dark Arts class, which ended in failure and further damaged his credibility.
Step-by-step explanation:
The 'spell' Peskipiksi Pesternomi was attempted by Gilderoy Lockhart in the Harry Potter series. Specifically, this happens in the book 'Harry Potter and the Chamber of Secrets', when Lockhart tries to use the spell during a Defence Against the Dark Arts class to round up a group of mischievous Cornish pixies. However, not only does the spell fail to work completely, it also serves to further diminish Lockhart's credibility as a competent wizard in the eyes of his students. The use of fabricated spells by Lockhart highlights his characteristic as a boastful and incompetent character in the series.