Could there be any possible action proving Yahweh to be cruel? Recently, one of my christian friends died of cancer. My Christian friends told me that Yahweh is very merciful. But if he got well, Yahweh would be merciful, too. 

So, HYPOTHETICALLY (see the note): could there be any possible real action proving Yahweh to be cruel? By real I mean not requiring faith in soul, heaven, sin and other christian stuff, clear to non-Christians.

In other words: If Yahweh did X, he would be cruel. - Is there any X from christian perspective (any doctrine)?

Note: I expect many downvotes here, but please help me improve it instead of closing votes: I don't mean this as holy war against Christians, I just want to know any reference to this question. Thank you.
Mercy is when judgment is withheld from those who deserve it.  God is merciful in that He oftentimes does withhold judgment and punishment from those who deserve it.  

However, God is not merciful in every situation.  If that were the case, He no one would ever suffer any penalty for anything they ever did.  Hitler and Stalin would be completely without judgment.  This is not the case.

There is a distinction between God being Love and God being loving.  God is love in that love is an attribute of God.  Loving describes His actions.  God is merciful (adjective), but God is not mercy.

Regarding the death of Christians, history is full of Christians who have died young and who have been killed for their faith.  Yet, in the truest sense, God was merciful to them--not in preventing all harm and death from them, but in forgiving them for their sins against God.  Death is the fate of all men, but death is not the end.  Mercy has to do with our sins being forgiven--not in us being freed from all suffering.