Often in depictions of Communism we hear people use the word Comrade a lot, especially in greetings. Was this the case? Were there any other quirks in Communist etiquette?
The word товарищ (Tovarishch) is translated into English as comrade. It was meant to be a kind of leveling out of titles that defied aristocratic conventions and has roots in other socialist/revolutionary contexts before 1917. In the Soviet Union it was used for both men and women.
I'm going to speak specifically to the case of the Hispanic left (both in the Americas and in Spain itself). Here Compañero (closer to partner) and Camarada (literally comrade) tend to be used by the left as opposed to historically more reverential titles such as Señor or Don.
This can be seen in the abundant Cuban cinema that has been produced since the Revolution. One classic, Memorias del Subdesarollo (Memories of Underdevelopment), has a scene in which the protagonist (an ex-bourgeois) attempts to defuse an issue at a police station. He attempts to say Compañero so as to get into the good graces of the pro-revolution policeman but instead receives a tart "I am not your compañero", due to his obviously bourgeois origins, underlining the political significance of the term. You can also read this news article explaining how compañero has begun to die out but has served as a politically charged expression of fraternity since the revolution.
George Orwell wrote Homage to Cataluña about his experiences during the Spanish Civil War, having fought on the side of the Republic. One thing he notesis that during the period when the left within the Republic was at crescendo that "No one called anyone else "Señor" or "Don" or even "usted"; everyone called everyone else "comrade" or "thou" and said "salud" instead of "buenos días"". The Republic at this time had the support of both Marxists and Anarchists against the revolt of the right who had captured around half the country. He also emphasizes that as time passed and the more radical left lost control of the Republic that Sr. and Don started making a comeback and Comrade started disappearing.
In closing, I´d like to emphasize that Comrade isn´t just "quirky etiquette" as you put it, but a leveling of the playing field by throwing out more reverential class based honorifics. While the term Don could be applied to anyone you had a particular respect for, it was invariably used for the wealthy and the powerful. Señor literally means lord and in Hispanic countries would be used frequently in conversation when you spoke to your social betters as a way of showing a degree of reverence (similarly to how in English someone may drop the honorific "mister" into conversation frequently if they want to show respect or demureness). Comrade, translated either as Camarada or Compañero, was a part of the cultural aspect of the revolution, wiping out class based honorifics for more popular and fraternal terms.
I'd also note that under the radical Jacobins, during the French Revolution, many honorifics were abolished and replaced with 'citizen' for similar reasons, so the contemporary Left would not be the first to use these terms.
It's not just Communists who use it either. The use of Comrade or Comrades as a form of address is still in use informally among the Labour party in the UK, even though the Labour party is social democratic at best. You can see in the search results of labourlist( A website often used to communicate news and option pieces around the labour party) that comrade is still in use.
China still uses 'Comrade' in official dispatch/addresses. Not as pervasively, but it exists. People working in Chinese governments will address each other as 'Comrades' when in a official meeting. They will also address each other as comrades in a joking manner in private. The term is still quite widely used.
In the GDR, the ruling SED party did encourage the use of the informal du (you) over the more formal Sie(you). In traditional German language convention, the informal tends to be reserved for personal settings while the formal is often used in workplace settings or ones other social situations where one party is superior, such as pupil/student or employee/boss (note this is a generalization and can be observed as much in breach in some areas- DW has a good explanation of the du/Sie dilemma ). The cultural authorities in the GDR portrayed this formal/informal division as a relic of Germany's inequitable society and did not represent the new worker's state created by the SED. In the workshops and in SED functions, the state encouraged the use of the informal to stress that all the citizens of the state were social equals. GDR state media often emphasized the term Genosse (comrade) and it evolved into a quasi-title for SED officials in print (such as "Rede des Genossen Walter Ulbricht," and so on). The SED privileged Genossen over the term Kameraden because the latter was more frequently associated with comradeship in an organizational context, often martial, exemplified by such the songs like "Ich hatt' einen Kameraden or "Alte Kameraden".
Ironically, this social leveling by language had something of an opposite effect upon the GDR public. Some East Germans associated excessive use of the informal with the various state functions and in private conversation the threshold for breaching the formal/informal divide was higher. Surveys after 1993 about the use of the informal noted that Germans from the GDR tended to use the informal more reluctantly than their Western counterparts.