In Islam it is obligatory for us to show kindness, respect, and obedience to our parents. The position of parents, and the mutual obligations and responsibilities, have been addressed in Islam in great detail. In fact kindness and obedience is so strongly emphasized that God has linked showing gratitude to one's parents with showing gratitude to God -

And We have enjoined on man (to be good) to his parents: in travail upon travail did his mother bear him, and in years twain was his weaning: (hear the command), "Show gratitude to Me and to thy parents: to Me is (thy final) Goal. (31:14)

Sadly we are living in a time where children speaking disrespectfully to their parents and about their parents, is the norm rather than the exception. However Islam places great emphasis on respectful and considerate behaviour to even our enemies, so to not uphold the obligations laid down by God to our parents is actually one of the major sins.

Treat  parents with honour & speak to them graciously & with humility

Thy Lord hath decreed that ye worship none but Him, and that ye be kind to parents. Whether one or both of them attain old age in thy life, say not to them a word of contempt, nor repel them, but address them in terms of honour. And, out of kindness, lower to them the wing of humility, and say:  My Lord! Bestow on them thy Mercy even as they cherished me in childhood. (17:23)

Be grateful to parents but do not obey them if they strive to make you associate things with God

...Be grateful to Me and to both your parents; to Me is the eventual coming. But if they strive to make thee join in worship with Me things of which thou hast no knowledge, obey them not; yet bear them company in this life with justice (and consideration), and follow the way of those who turn to me (in love): in the end the return of you all is to Me, then will I inform you of what you did (31:15)

These verses make it clear that we must honour our parents, appreciate their sacrifices and efforts for us, and do our best for them. This is required regardless of whether they are Muslims or not.

Be good to parents and everyone else who you meet

Serve God, and join not any partners with Him; and do good- to parents, kinsfolk, orphans, those in need, neighbours who are near, neighbours who are strangers, the companion by your side, the wayfarer (ye meet), and what your right hands possess: For God loveth not the arrogant, the vainglorious;- (4:36)

If the Quran tells us to be good to a stranger how can we even think of disrespecting our parents?

Hadiths
Let's see what Prophet Muhammad   said about parents in the authentic Hadiths. Whatsoever the Prophet gives you, take it and whatsoever he forbids you, refrain from it. - Quran 59:7

Anas narrated from Prophet Muhammad  about the major sins. He (Mohammed) observed: Associating anyone with God, disobedience to parents, killing a person and false utterance. (Muslim)

One of the dearest deeds to God is being good & dutiful to parents

Narrated 'Abdullah: I asked the Prophet  "Which deed is the dearest to God?" He replied, "To offer the prayers at their early stated fixed times." I asked, "What is the next (in goodness)?" He replied, "To be good and dutiful to your parents"...(Bukhari)

Being dutiful to parents is one of the keys to enter Paradise

Abu Huraira reported Prophet Muhammad as saying: Let him be humbled into dust; let him be humbled into dust. It was said: God's Messenger, who is he? He said: He who sees either of his parents during their old age or he sees both of them, but he does not enter Paradise (because he has been undutiful to them). (Muslim)

Acts of kindness we can do for our parents after their death

While we were with Prophet Muhammad of God . A man of Banu Salmah came to Him and said: Apostle of God is there any kindness left that I can do to my parents after their death? He replied: Yes, you can invoke blessings on them, forgiveness for them, carry out their final instructions after their death, join ties of relationship which are dependent on them, and honour their friends. (Abu Dawood)

The High Status given to Mothers

A man came to the Prophet  and asked him for permission to join a military expedition. The Prophet  asked him if he had a mother, and when he replied that he had, he said, "Stay with her, for Paradise is at her feet." (Ahmad)

Summary

Sometimes we may take our parents for granted and overlook their importance. As Muslims we should constantly be alert to guard ourselves from sins, however, are we guarding ourselves from one of the biggest major sins? Are we honouring and respecting our parents as per their right? Or are we neglecting one of the deeds most dearest to God?  Right now the choice is ours!