It is grammatically correct, yes. It is an odd statement and the context would help to understand if the sentence clearly expresses what it is intended to express. If this is a character stating his personal philosophy in regards to conserving his energy around talking about things that may or may not ever happen - perhaps a better choice of words would be: "I never like to talk about events that are not inevitable."

If you add a period at the end, this sentence is grammatically correct, but it is odd. The sentence does not make much sense because it has so many negatives. It would flow better to say, "I like to talk about things that are impossible." Inevitable is a somewhat negated word. This word means something is guaranteed to happen. In the US, we don't use the word "evitable" to mean something that will not happen. You would use "impossible" to describe something that cannot happen. I hope this helps, it is hard to fully understand the question.