#killallmen doesn't seem to be very popular, used much more by people complaining about it than actually using it:https://twitter.com/hashtag/killallmen
And has been around much longer than this whole "SJW" bullshit.
Plus, it's considered satirical:
Thingtoocoolforyou ‏@Thingtoocoolfor Aug 17
Satiricial hashtag #killallmen gets people more angry than the actual murders of women and girls
plain eyre ‏@thewordy
i joke "#killallmen" & dudes in my mentions think i'm serious i say "stop harassing me" & dudes think i'm joking