You need to stop acting in such a puerile manner and act your age.
She was making puerile excuses about not wanting to get up for school this morning. That sentence works because it means to be trivial or childish about something.
youthful; juvenile silly
To answer the question: "What sentence could you use for sneer?" One could answer: "I sneer at your puerile attempt at a question." (Seriously, puerile and sneering do go rather well together ... sneering is that ugly facial thing that people do when they can't help their face but show how below themselves they believe you to be ... puerile is the usual [internal] insult that goes with the sneer face ... sneering is all about contempt ;))
You need to stop acting in such a puerile manner and act your age.
immature
Belonging to childhood; juvenile. Immature; childish.
preposterous (:
premature and puerile, petty
I think you mean puerile. It means immature or childish.
A synonym for "puerile" is "childish." Both terms describe behavior or attitudes that are immature or lacking in seriousness. Other synonyms include "silly" and "foolish," which also convey a sense of naivety or triviality.
Adolescent, childlike, childish, inexperienced, puerile, tender...
Cyril. Although there's the alternate 'ile' ending-- puerile, sterile, etc.