Can you deny giving someone a gift?

If you are saying he is giving away games but picking people, then its not allowed. but im not sure

report him

He can reroll but if he picks on his own then I doubt it will count as being on Steam Gifts. And if it's public then there cannot be any special rules.

By the rules you can only do this in private giveaways. In public there should be no restrictions.

Even so, if the guy refuses to give the gift, he may well do so and the only thing that can happen to him is a bad feedback.

More often than not, these requirements are of good behaviour, ex: mustn't own base game from given pack, mustn't have abused bundles, etc.

You can always refuse it, as long as you don't mind a Not Received. However, it's best to make a support ticket for a reroll if you have a legitimate reason not to.

Well if you want the realist explanation then it's your gift and you can do whatever you want with it, but however you have 100% of being banned from the site, but the gift still stays in your inventory, so no matter what happens the gift is still yours.

Now for the other explanation that follows the rules, Yes it's not allowed to do this in the rules unless you've asked an administrator/mod about it and they confirmed you can do this, thing that says $200 worth of gifts is his own choice, if you giveaway bundles you'll only have $30,00 maximum and he set the contributor value to 200 so that's allowed, but I don't see anywhere that he'll be choosing the winner by himself so I don't know where's the part where he's breaking the rules.

From the FAQ
"Extraneous/special rules for giveaways require moderator approval. Public giveaways cannot have any special rules."
If this is a private giveaway (Do contributor giveaways count as private?) then he is well within his rights.

Well, did you read the FAQs, if you read it, then you would know the answer to your question and would know that you are in a violation of the rule yourself.

Well, I guess you could report him to the mods. Our massive army of mods.
It's the wild west right now.

well i got my answers, thanks