acting like you know something when you actually have no idea.

a stupid student

Stupid people, as a group.

Reproduce rapidly, but tend to die frequently. Fundamentalism is largely confined to this group. Not the cause of warning label proliferation; that is the result of ambulance chaser lawyers.

The more linguistic and non-dictionary version or "more stupid" which makes it easier to say

What you feel after you do something totally unnecessary, but you need to do it anyway and something you didn't expect happens, and it's only afterwards that you realise what you've done. Usually involves a person of the opposite sex and/or someone you got a crush on.

Something dumb, unintelligent, or generally just idiotic.