The customers violent reaction, I believe, is not the typical reaction someone would give. Maybe that dude just had a hard day, or has other mental health issues which were not considered.
I probably wouldn't say anything because I wouldn't want to hurt anyone's feelings, but I've been around some stanky arse people before where I actually thought I was going to vomit. My sense of smell is dull, so when even I can smell ya, its bad. Peeeew!
Aside from me not wanting to hurt anyone's feelings, I think its ok to approach the subject of body odor with people provided that its in the right way, considering, as mush as possible, the persons cognitive status, culture, lifestyle, and emotional/mental health and well-being. Just walking up to someone to say, "Hey dude, you need to take a shower," is inconsiderate, disrespectful, and just not cool.