Well, I can't really see them getting into a war with a country they don't border, so by my map, that leaves China, Laos, and Cambodia. China certainly wouldn't count as "inferior technology", and, depending on what exactly you think happened in 1979, the Chinese were arguably the "USA"(ie. the humiliated party) of that little melee.
I'm not really aware of how the Vietnamese people felt about their status relative to their Khmer Rouge rivals. Was the ongoing warfare in the 1980s and early 90s regarded as a humiliation for Hanoi? I dunno, as you say, they WON, and considering that the Khmer Rouge had China, the USA, and the UK in their corner, I'd say the Vietnamese(granted with some Soviet support) put on a pretty impressive show.
Don't know anything about Laos. For now I'll assume that their relative obscurity indicates that they're probably not much of a military power, so if Vietnam got its ass kicked by them, yeah, it probably would be a humiliation. But of course that has to be balanced off with the possibility of Laos beating Vietnam to begin with, which seems pretty remote to me.
One thing I'll say is that I think a big part of the reason the US in Vietnam lost was because the American people(not without justification) had simply given up on wanting to fight the war. Yes, the North Vietnamese fought with great tenacity, but that had to combine with an unwillingness of the American public to continue facing that tenacity, in order to produce the end of American involvement. If someone had been able to sell the public on "Sure, the Vietnamese are tough, but we'll just keep bombing the hell out of them until there's no one left", it probably could have worked.
What sort of attitudes toward foreign wars you had among the Vietnamese in the the 70s and 80s, I don't know. Obviously, it wasn't much of a democracy, so the government didn't have to worry as much about elections or protests in the street.