"The way you use the word 'God' does not show whom you mean but rather what you mean." (Wittgenstein)
The most important element of monotheistic religions is the prohibition on idolatry. Idolatry is the raising up of some created facet of the world (so either an object, an ideology or a value) and giving it the importance that should be reserved for the creator alone. It is about getting our priorities wrong. Terrible consequences always follow from idolatry.
There are a number of ways in which to discern if idolatry is taking place. The most straightforward comes when actually using the language of God. For the rule is: the living God cannot be the member of any set. If you are attributing something to God which can also be attributed to another object or value, and you are not prepared to entertain any negations or qualifications to that attribution, then you are engaged in idolatry.
So, for example, we can take the claim that 'God exists'. This makes God a member of the set of 'existent things'. Thus it is a theological mistake. God is not a member of the set of 'existent things'. It would therefore be strictly accurate to say that God does not exist.
Or take the set of 'good things'. God is not a member of the set of 'good things'. It would therefore be strictly accurate to say that God is not good.
And so on.
This undoubtedly will sound like 'cobblers' to the humourless atheist - but that is, I argue, because they have a restricted understanding of what it means for language to 'make sense'. Theologians do different things with language. But I'll say more about that, particularly the nature of analogical language, in due course. For now I just want to emphasise this basic rule of theological grammar: all idolatries are prohibited. God can never be the member of a set.
One defining feature of humourless atheism is that it depends upon the violation of this rule.