The aftermath of a man's orgasm will "make a mess" if it is not contained by a condom, a mouth, a vagina, or an anus. In other words, it is allowed to spray and land either on the man or on his partner or partners or on the sheets or the floor or anywhere else.
My girlfriend never wants me to make a mess, even when I am masterbating around her. When I masterbate, I have to call her over when I am ready and she has me cum in her mouth after which she swallows so I don't make a mess.
to take a shit
Man, I just made a mess in the bathroom. Careful.
co-mingling of body fluids, wet spot, etc
lets' make a mess!