Excerpts from Global Nerdy:
A bug that isn’t reproducible and has been sighted by only one person.
A bug report with no error message or “how to reproduce” steps and only a vague description of the problem. Usually contains the phrase “doesn’t work.”
A bug report submitted by a user who thinks he knows a lot more about the system’s design than he really does. Filled with irrelevant technical details and one or more suggestions (always wrong) about what he thinks is causing the problem and how we should fix it.