It's fine until you change a vague statement about "most" relationships (which obviously means outgroup-people's relationships) into a specific one about people in the conversation, or friends of people in the conversation, or other ingroup members. At which point, I'd say it's just offensive, not taboo. Offensive, hard to justify, based on the outside view when people with inside view information are around... yeah, probably instrumentally unwise to say most of the time, too.