Earlier quoted context omitted.
> systematic oppression > Do the same to an unprivileged minority and it is potentially life threatening. There is no comparison. Racism must be systematic in order to be 'real' racism? Instances of racism must be comparable to one another in severity in order to be 'real' racism? These implications of severity and comparability are entirely your own invention. anewguy99 was not suggesting anything of the sort, you h…
See: Derailing. When instances of oppression occur, the most important thing to do is not point out the hypocrisies of the victim. It's not to whine about the oppression that YOU have to deal with yourself. It's not to compare your minor suffering to their systematic bullying. Everyone suffers, everyone has their own battles. Now is not the time to dredge it up as if it's more important, or just as important as what…
What you mean when you say "racism" is not what the parent means. The dictionary definition[1] of racism is actually quite broad and basically says that you're both right - the word "racism" can be used to describe a systematic system of oppression of racial minorities, but it can also be used to describe any instance where race is used as a discriminating factor.
You're not going to persuade very many people by simply asserting that the word means what you think it means, when other reasonable people could disagree about that meaning. You'll end up in pointless semantic arguments, and if you're doing this on HN then you'll be arguing with people who can make some very nuanced arguments about semantics.
There is a whole discourse about race, privilege, oppression, gender and so on which has acquired its own vocabulary, often by applying very specific meanings to words which have historically broader meanings, and which places emphasis on systematic or aggregate effects of oppression/privilege. Communities which are not steeped in this tradition do not share these word usages or these emphases; the average HN user is going to see a reference to "...white dudes..." as "racist" because it's a phrase that invokes race and gender when these factors are otherwise irrelevant, and they're going to focus on the individual case rather than where this fits in the aggregate sum of all racism/sexism across humanity.
In other words, your average HNer is probably follows deontological ethics[2] and is likely to evaluate individual instances of behaviour according to general rules. If invoking race is bad, invoking race in relation to white people is therefore bad, and therefore the "white dudes" comment is bad. You can't easily argue (to a deontologist) that it's "not racism" because this means that sometimes the "rules" don't apply.
Now, I'm not saying who is right or wrong, only that it's something that reasonable people can disagree about. I doubt that there is a right or wrong. My belief is that it should not be impossible to agree on how to tackle discrimination, but in order to engage everyone in doing so we'll need to appeal to a range of different ethical viewpoints, and trying to argue that the other person's ethics are simply wrong is unlikely to be persuasive.
[1] http://dictionary.reference.com/browse/racism?s=t [2] http://en.wikipedia.org/wiki/Deontological_ethics