Interesting dilemma. Admittedly C's and D's are a far cry from a 3.86 (which is basically nothing but A's with a few A-'s accidentally sprinkled in). You nevertheless gradumagated cum laude, honors society as well, and I imagine you were on the honor roll plenty of times. That oddball quarter will probably get noticed, but I don't imagine it will be much of an issue - it clearly stands out as anomalous (even without you explaining anything). So, on balance, unless that quarter was heavy in quant classes (AND your other quarters were not -- e.g. they might misinterpret it as a math weakness) I probably would leave it alone.
If it absolutely eats you up though, there's nothing wrong with saying something about it. I'd just keep it REALLY short and really sweet though. For two reasons - 1) I always say that because otherwise people tend to say a bit too much and be a bit too honest anyway 2) It's already obvious that it isn't representative of your skills, so you don't have to worry about explaining it much, simply answering the "Gee, wonder what happened in that quarter" is more than sufficient.
I'd say something like "personal challenges that distracted me from my studies", or you can say you came out and say something like "the difficulties that come with that kind of disclosure, particularly among individuals I had considered friends, presented formidable challenges that regrettably impacted my academic performance. Nevertheless...bla bla". I'd shy away from talking too much about how people treated you, death threats, going into a depression, etc. I'm not trying too belittle your challenges, simply suggesting that sometimes less is better. (I recognize some people might suggest to pull out the depression card, i'd personally avoid it as I think its a bit too personal)