From the Mahasatipatthana Sutta:
I don't see how that would ever lead to ejaculation.Again, a monk, when going foward or back, is clearly aware of what he is doing, in looking forward or back he is clearly aware of what he is doing, in bending and stretching he is clearly aware of what he is doing, in carrying his inner and outer robe and his bowl he is clearly aware of what he is doing, in eating, drinking, chewing and savouring he is clearly aware of what he is doing, in passing excrement or urine he is clearly aware of what he is doing, in walking, standing, sitting, falling asleep and waking up, in speaking or staying silent, he is clearly aware of what he is doing. So he abides contemplating the body as body internally, externally, both internally and externally ... And he abides independent, not clinging to anything in the world. And that, monks, is how a monk abides contemplating body as body.