1. The Correct Aqeedah (Belief)
Things that Invalidate
your Shahadah

2. Associating Partners with Allah
Allah says:
"Truly, whosoever sets up partners with Allah, then Allah has forbidden the Garden for him, and the Fire will be his abode. And for the wrongdoers there are no helpers." (5:72)
Calling upon the dead, asking their help, or offering them gifts or sacrifices are all forms of shirk.

3. Also Disbelief:
Setting up intermediaries between oneself and Allah, making supplication to them, asking their intercession with Allah, and placing ones trust in them is unbelief (kufr).
Anyone who does not consider the polytheists (mushrikeen) to be unbelievers, or who has doubts concerning their unbelief, or considers their way to be correct, is himself/herself an unbeliever (kafir)
Anyone who believes any guidance to be more perfect, or a decision other than the Prophets decision to be better, is an unbeliever. This applies to those who prefer the rule of Evil (Taghout) to the Prophets rule.

4. To believe the following also invalidates your Belief:
To believe that systems and laws made by human beings are better than the Shariah of Islam such as:
To believe Islamic laws are backwards or outdated
Women believing that the Hijab is primitive
Believing that the role of women and men have changed

5. Also to say that the punishments prescribed by Allah are out dated invalidates your faith:
Example:
To cut the hand of the thief
Punishment for adultery stoning
Punishment for fornication 80 stripes

6. To believe that it is permissible to make things lawful that Allah made unlawful
Examples:
Allah has outlawed Alcohol, Gambling, Adultery, Fornication, Prostitution
To say these things are permissible many scholars say the person has become an unbeliever

7. Also to hate anything that Allah or the prophet made lawful will invalidate your belief:
Allah says:
"This is because they hate what Allah has sent down, so he has made their deeds fruitless" (47:9)
Examples:
A person hates Hijab, hates the prayer, hates fasting during Ramadan

8. To ridicule any aspect of Islam or the believers or Allah book invalidates your belief as well:
Allah says :
"Say: Was it Allah, and His signs and His Messenger that you were mocking? Make no excuse; you have disbeleived after you had believed." ( 9:65-66)

9. Practicing Magic also invalidates ones belief:
Included in this, for example, is causing a rift between a husband and wife by turning his love for her into hatred, or tempting a person to do things he dislikes using black arts. One who engages in such a thing or is pleased with it is outside the fold of Islaam. Allaah says:
" But neither of these two (angels, Harut and Marut) taught anyone (magic) till they had said, Indeed, we are a trial; then do not disbelieve. ( 2:102)

10. Helping the Unbelievers against the Muslims also invalidates belief
Allah says:
"Whoever among you who takes them as allies is surely one of them. Truly, Allaah does not guide the wrongdoers."
(5:51)

11. To believe that some are allowed to deviate away from the Quran or sunnah makes one an unbeliever
As by the word of Allah:
"And whoever seeks a religion other than Islam, it will not be accepted of him, and in the hereafter he will be from among the losers."
( 3:85)

12. Finally To turn completely away from the religion of Allah neither learning its precepts nor acting upon it.
Allah says :
" And who does greater wrong than he who is reminded of the revelations of his Lord and turns aside therefrom Truly, We shall exact retribution from the guilty." ( 32:22)
and He [swt] also says:
"But those who disbelieve turn away from that about which they are warned."
It makes no difference whether such violations are committed as a joke, in seriousness or out of fear, except when done under compulsion (i.e. from threat of loss of life )