There's nothing wrong with asking questions without self-deprecation, but if you're going to self-deprecate, try not to use hurtful language.
Now I see your point, though, he is associating his slowness-to-the-punch with people who are unfortunately physiologically slow-to-the bunch, and according to you this type of lateral association is bad because...?
Because it is shameful to be wrong or ignorant, and therefore associating the shameful act of a non-retarded person with the unshameful reality of being retarded creates a subconscious association between being retarded and shame--- is that it?
If so, isn't it harmful to consider being publicly wrong or ignorant shameful? Should we not have patience with others who know less?
I understand there's a spartan-esque utility to being brutal in a highly competitive skills-based situation (like most engineering). So I am unsure as to where to position myself with this question!
Shed some light?
Some people have mental health issues. Throwing "retarded" around simply make those people feel bad.
How hard is it to use a different word that won't put a load on someone's life?
It's often hard to have this discussion without it devolving into an argument over "political correctness" [0] so hopefully that can be avoided.
Easiest answer is that the term retarded originally was an acceptable term for people with disabilities, but now has a negative connotation, and when used pejoratively as OP did carries the (possibly unintended) implication that people with disabilities are of less value.
I think Wikipedia entry on Retard (pejorative) [1] is a good summary.
It's also worth mentioning "ableist language" and "ableism" here. [2]
[0] - https://en.wikipedia.org/wiki/Political_correctness
Anyway, it's not shameful to be wrong or ignorant. That's why I said that there's nothing wrong with asking questions without self-deprecation.