the answer is a bill of attainder
The US Constitution forbids legislative bills of attainder. They were forbidden to keep people from being punished for something without a trial. This is found in Article I, Section 9.
The constitution is not a 'negative law' overall it is a 'positive law' that is to say, there are very few things that the constitution forbids, in all it is a grant of or establishment of government and a limit on what they can do, it also acts as a statement of rights that existed before the government was formed, and limits governments ability to infringe on these rights.
As an example of a "forbidden act:"
"...no religious test shall ever be required...." (article 6)
In examining the amendments:
"Congress shall make no law respecting an establishment of religion..." (1st Amendment, part 1).
While each of these parts stand alone as prohibition, together they form the basis for "a inseparable wall between church and state" - quoting the Supreme Court, quoting constitutional authors on the subject. However this provision is violated in our money and pledge - "In God we Trust" appears on all money, its provision was added by a church sponsored initiative, who happen to name their worshiped deity "God."
"....or prohibiting the free exercise thereof" (1st amendment, Part 2)
While this clearly prohibits a law against any religion, the US Government banned a Native American ritual known as "[the] Ghost Dance" in 1890, and the law was not repealed until 1976.
".....or abridging the freedom of speech," (1st amendment, part 3)
This part, when combined with or in light of part 5 & 6 give people the right to protest; this right however is prohibited by license, licenses for acts that do not meet the approval of certain members of government are denied on a regular basis.
That is not to say that the right of free speech is unlimited; there are limits (from an ancient viewpoint) on "hate speech." This form of speech is commonly defined as speech that calls for a violent action against another, or that incites a violent reaction.
To attempt to put this in perspective: if the KKK were to apply for a license to protest in a predominately black section of a city; and it is known that the KKK call for acts of violence towards blacks, then there is no right in this context.
"....or of the press;" (1st amendment, part 4)
This part extends the right of free speech to news services, with the same limits set out above - but with an added responsibility that the news stories must be true based upon the facts known at the time. This is another 'right' that is abused by all sides.
"....or the right of the people peaceably to assemble" (1st amendment part 5)
This part is intended to restrict the government from infringing on the rights of groups who's aim is contrary to government goals. While it stand alone it is also enforced by the next section.
"....and to petition the Government for a redress of grievances." (1st amendment part 6)
This section is intended to establish two distinctive rights; the first is that a person may bring suit in a court of law against the government, and that the people may form groups to demand redress (redress can take many forms).
Now when the "First Amendment" is put back together the overall intent is to ensure that the people retain the rights (listed) so that they can take a hand in government. This amendment of course works with other amendments in the same way, as in they support the people in their ability for that goal.
I must also caution you that this is a very limited reply to a very large subject. Justice Story of the US Supreme Court wrote a book about this subject, it is authoritative because of his position and his relation(s) with James Madison.
This is NOT a small book, it is huge and will take the average reader a very long time to read, it is also complex in that it deals with legal concepts of the constitution that were still alive when it was written.
If you really want to learn, there is a link below this to the actual book that you can read online or download and read for free.
Excessive force
The question COULD be more speciofic, but among other things it forbids the use of cruel and unusual punishment.
Clause 3 of Article I, Section 9 of the Constitution forbids the federal government from passing EX POST FACTO laws, and Clause 1 of Article I, Section 10, forbids state governments from doing the same.
Unless a constitution forbids it, as many as you wish
There have been thirty-three amendments to the US Constitution since it was written. The First Amendment specifically forbids the establishment of religion.
There are no nobility ranks in the United States. The Constitution includes a provision that specifically forbids US citizens from holding any rank of nobility.
The 8th amendment to the US Constitution prohibits cruel and unusual punishments.
Keep Militia
The Eighth Amendment to the Constitution forbids excessive bails/fines and cruel and unusual punishment.
The practice of untouchability.
The US Constitution forbids states to coin money. They also forbid states to allow anything other than gold or silver to be used as legal tender.
The U.S. Constitution forbids any law that conflicts with existing Federal laws. It also forbids any law that violates the Constitution itself.
Their new constitution forbids war.