The definition of tolerant is to be accepting of things and perhaps able to endure unpleasant things. However, to be not tolerant can be expressed two ways depending on the specific lack of tolerance being discussed.

Intolerant: Not accepting, allowing or enduring something/someone to exist without interfering, complaining or hindering.
A racist person is intolerant of other races living in their country.

Intolerable: A situation that can’t be endured or continued. 
After time a worker may find it intolerable to work 100 hour weeks and be criticised by their boss.

Think of the two words like this: He is not able to tolerate a situation but the ant chooses to be intolerant.