1. A phrase of exclamation said when you receive exactly what you need exactly when you need it.
2. A phrase roughly equivalent to: 'fucking cool!!'
To use it in a sentence:
1. 'Thanks for pulling through for us. That was so damn clutch
2. 'Aw man, didja see that? That was so damn clutch
antonym - so damn garbage
Alternately you could say, 'so fucking clutch,' instead of, 'so damn clutch.'