How would you go about it? There are so many different hypothetical situations, so just choose a situation you had to deal with in the past or at least envisioned dealing with.
When I say "ambush," I mean sneak up behind and choke out or other bare handed attack to disarm the person you are jumping. There was this one time I was considering jumping this frat guy who was of a similar weight (a situation where i didn't want to have to fight the whole frat), anyways issue blowed over. But I was thinking, "shit, it would be hard to ambush this guy on campus and actually get away with it. "
The purpose of the ambush is also being stealth and disabling the person before they could bring attention to the situation by creating a scuffle or noise. Also would consider the logistics of needing to wear a ski mask. So the guy that wronged you can't see his assailant.
Despite the image, i'm being serious. Unless you're a cop. Then this is all a joke.