Are you offended when

someone describes a living (or dead) person, an imaginary character or an object as "God"?

A silly question. Personally, I choose to not care and nod in agreement. If I do so, would it count as a sin?

Let me use a sentence for the purpose of adding clarity to my question. Freddie Mercury is the God of rock music.

That question is an oxymoron. Freddie Mercury is dead, but God is not.. lol

I would not say that I am offended, but I do think it is taking God's name in vain, and should not be said.

May I ask how one is "born a Christian?"

Mayhaps you should start there. Resolve that issue, and the one you mention in the OP will resolve itself methinks.

No bother here. Because even the bible mentions that there are (false) gods. In most mythology those are considered gods. The word god is not exclusive to God Himself but a reference to a deity. So the term god of rock and roll has zero to do with blasphemy against God because the intent of the word is not even spiritual in nature but rather descriptive of how the individual is viewed in his culture.
And since this usually refers to nothing more than great respect for the individual, and not actual worship, it's a feasible term.

Saying something like what you used as an example wouldn't bother me unless someone was insane enough to say God not god.
There's a huge difference between equating someone with A god and saying they are God.
That said over the top statements do annoy me but it takes way more than that to offend me lol.

When someone calls Freddie Mercury the god of rock music, it's clear they don't mean that Freddie Mercury is THE God. So, no.

After I gave up cigarettes, I told people that I discovered they were a "god" in my life. Sort of like my "god of comfort".

That said, there are many ways to use the word god. And different people mean it different ways. I meant it as in idol that I depended on. To others, that same cigarette might not be their "god", but it was for me.

To pick at nits, it's "god" with a lowercase G. . And yes, I get quite annoyed when people say that in a casual way. But then, I get annoyed when people use any random, meaningless expression without thinking it out.

When people call someone God, I view it as a way as saying that person is the GOAT. I t doesn't bother me as well

I feel making a statement like the god of rock and roll is bringing God The Father down to a human level which is concidered blasphemy.
When Elijah looked at the many gods of the Greeks he saw the unnamed god and enquirer why there was an unnamed god.
The people brought the unnamed God to the status of their other gods.
Be careful not to do this.
If someone unsaved were to here those words they would assume you think the god of rock and roll and the God you claim you know are no different

It's irrating to listen to someone give so much praise to a human, it's idol worship, they did nothing of any real significance and value.

Who can change a culture from cannibals to one that shares food with their neighbors?
Who can turn a heroine addict into a minister?
Not Freddie Mercury. Not Elvis. Not any big league sports star. It's Jesus Christ! It's just annoying to hear talk of anyone being the god of anything.

I probably wouldn't even notice. The typical English slang phrases are not something typically given a lot of thought.

It is not a statement I would make but hearing it wouldn't affect me in any manner.