metaphora

Metaphors can be as useful as a hole in the head.
They can also be as ambiguous as a hole in the head, because headholes could be bad (like  a mortal wounding) or good (like a mouth, into which bacon can be inserted).

Here are some examples, allegedly written by real life high school students.  So you know they're going to be good.

You can also tell that the individual who compiled these thought they were smarter than the high school students, when in reality, they called the following statements "analogies", which is not entirely untrue, but "metaphors" would have been a better choice.

It makes you wonder how much they paid attention in their high school English classes.

You are no doubt dumbstruck by the literary prowess of alleged high school students.  I find the ninth one there to be quite meaningful, for example.

(Actually, I love it.  It's hilariously demonstrative of her lack of vocabulary.  My love for number nine is not sarcastic.)

This reminds me of one of my favorite metaphors, from The Red Badge of Courage.  It goes something like this:
"The red sun was pasted like a wafer in the sky."

I'm going completely from memory there, so it might not be verbatim, but I find it hilarious.  HILARIOUS.

So I guess the lesson here is that metaphors are either effective, or hilarious.
And if you're Mark Twain, then perhaps your metaphors are both.