Verb. The act of hitting the back of another persons knee when their knee is locked, causing the person to stumble and possibly fall. There is also the muthasucka twofer where when you perform the act, the individual yells out in surprise, "muthasucka!".
slang word, actually spelled m.o.t.h.e.r.f.u.c.k.e.r.; meaning
1.)a guy who has sexual intercourse with his "mutha" --> mother.
2.)an asshole, even worse than an asshole so the term muthafukka is what he deserves
3.)all the stupid people who read this shit
1.)"Ey I saw your mutha last night! she's a real MILF!"
"'course she's a milf, why you think i fuck her every night?"
2.)"hey, you're a fuckin' jerk!"
"at least not as worse as you, muthafukkkka!"