回复：问一严肃问题：朋友在国内说要往我账户上打5万美金，因他最近

Well, if your friend's money is illegal income and you helped him as said, you are involved in money laundering. Even if the income is legal, your friend may be evading income tax and you are in trouble to help him.

At least you can sign an agreement with your friend to say the following:
1) It is your friend's responsibility to warrant that this money is legal and all associated tax paid.
3) The agreement should describe the transaction in detail. The money that you are receiving is not your income to avoid income tax. The money that you are giving back to your friend is not gift to avoid gift tax.
This agreement may NOT save you from all trouble.