What is up with words that are opposites, but mean the same colloquially.

For instance:

That sucks/blows: Something is bad.

It's all uphill/downhill from here: Bad things are going to happen.

Slim/fat chance: you have little chance of something happening.

I've come up with this list over the past few months and for some reason they really bother me. Can anyone think of examples I'm missing?