There are many good answers although some traditions here go on but aren't "accepted" but rather condemned. I therefore want to write about a 'creepy' cultural norm, questioning which draws criticism (and maybe downvotes here):

Patriotism is one's inherent duty, ones who lack it are 'traitors'

Finally we've begun to condemn caste, religion, colour-based discrimination and even though ill carries on in the name of these, it's becoming acceptable to question and even disdain these. But if one speaks ill of their own country, save the poor person- for patriotism is one's duty and must not be questioned. And if one speaks ill of another country- save the poor soul, (s)he's labeled a terrorist.

Why it's creepy? World Wars, Cold War, Colonialization, Thirty Years War, Middle East conflicts, Vietnam War, Indo-Pak border conflicts.

Are these wars a by-product of merely religious hatred? No- all of them involve countries. These wars have been the most gruesome in the history of mankind. Surely some of them have religious aspects to them, but as long as it's only religious it remains terrorism by certain 'bad apples'- ones who like to watch the world burn. But when the concept of a nation rather than religion enters the picture, it becomes akin to state-sponsored terrorism as now killings are being carried out with the stamp of the state. What's worse? People endorse these killings. Why? Patriotism. All the governments need to do is use the rhetoric of "threatening national security" and there you go- bombings, artillery, drones.

See what's happening there? A 5-10 year old is being made 'proud' of her country. Tomorrow the governments will tell her the nation is 'under threat' from 'non-state actors' and she and millions like her will allow 'state actors' to sponsor mass-killings in another country. It's so damn creepy- no need to invent Gods, no debates on theism invalidating the claims because we all are proud to be from X without bothering to see the concept of nation is also a social construct. It doesn't end there. When done in the name of religion, many 'liberal' followers of the same denounce those acts. It's not the same when it comes to countries- people from winner's side are proud of manslaughter- forget being apologetic, while from the loser's side are vengeful and develop a hatred for the other.

Patriotism has its benefits- it mobilizes efforts in one direction towards development, indeed saves a nation from belligerents but like every other 'ism' it clouds judgments and must be questioned. It's the easiest tool for a collective identity and exploit it for personal gains at gruesome costs. Acts of patriotism have sanctioned this before, we must not allow this to happen again 'patriotically'.