Personally, I don't have a problem with ASCII penes in CN, but
in a prior incarnation of this discussion it was established that my standards for NSFWness are significantly more liberal than average. As such, I'm probably not the best person to make that call.
The main source of contention with regard to whether ASCII penes are considered NSFW is, as far as I can see, a matter of definition. Those arguing they should be treated the same as certain words or symbols are considering them to be text, while those favouring treatment along with photographs are considering them to be images. I contend that they are both, and that this issue therefore cannot be taken as a matter of consistency among text or images.
In that light, let's discard any arguments for consistency and instead consider ASCII art in terms of its potential for harm if it is viewed in a sensitive context. Personally, I think it's reasonable to expect people to avoid browsing CN in any situations where ASCII art is likely to cause trouble, given that such environments are somewhat uncommon and that we don't want to start banning things just because they offend someone in an office somewhere in Idaho. On the other hand, it is reasonable to take a firmer hand with regard to actual photographs of genitalia, because those are more widely regarded as taboo in the workplace.
In between those two extremes sits drawings. As in the thread I linked above, I still think drawings of nudity are perfectly acceptable in CN, but if most people disagree then I'm happy to swing the other way on that issue.