An example of presumptuous is assuming that you will win the city wide spelling bee just because you scored 100% on your last spelling quiz.
Felt it was presumptuous of him to assume they had become friends.
Origin of presumptuous
- Middle English from Old French presumptueux from Late Latin praesūmptuōsus variant of praesūmptiōsus from praesūmptiō presumption presumption
From American Heritage Dictionary of the English Language, 5th Edition