The story
The first sense derives from red as an adjective meaning associated with or supportive of communism. The second sense derives from the Red Wedding scene in A Storm of Swords by George R. R. Martin.
Etymology from Wiktionary, CC BY-SA 4.0.
red wedding
Today it means: A wedding ceremony in the Soviet Union in which the couple pledged loyalty to the state or communism in addition to reciting marriage vows. Full definition →