What I wrote about this at the time:
Eleventh entry in this year’s #Decemboobs, an annual challenge for cartoonists and other artists to get better at drawing breasts by creating a drawing a day from reference. Most of the time, I don’t draw just the boobs, but for days when I’m in a hurry, I always have a few boobs-only references filed away. This has been one of those days; in fact, I drew this yesterday as the second image of the day because I anticipated a long day at the day job. Instead, I got sick and spent the day in bed with a splitting headache. Either way, it was a good thing I’d already done this image. The source is a subreddit called normalnudes, in which men and women of all ages, shapes, races and sizes share nude images of themselves, usually anonymously, for comparison, reassurance and (if asked) critique. The reference for this one is https://www.reddit.com/r/normalnudes/comments/7djaqb/got_my_nipples_pierced_last_week_and_i_am_so_in/Done in pencils on illustration board as before.
This one hasn’t aged that well; I can tell looking at the reference again that the torso is too small and the shoulders and arms too wide. But, that’s what you get when drawing traditionally: your options for fixing faults become more limited.