I recently had to cross someone up. It was a situation where I was just going to originally let it go and just cut the person out of my life. However, this person decided they were going to brag to nearly everyone who would listen on how they screwed me over. So people started trickling in to me telling me of how this person thinks it's so funny what they did to me. So I decided they needed to learn what a conjure worker can do and I crossed 'em good.. Within a week this person broke their finger and it swelled up to the size of a pickle. Breaking the finger also caused this person to miss a very important event they were supposed to attend. So I'm pleased with the outcome.
The point of me writing this is that even though I've gotten my revenge this person has no clue that I crossed them up. When you literally have to cross someone up you need to do it with the knowledge that, 1.) you may not hear of the work manifesting, and 2.) the person likely won't put two-and-two together and know this is because of what they did to you. Unless you want to go the route and tell the person that you crossed them up. I don't go that way but if that's your taste, power to you.
One more thing, I strongly advise people to not push for more than what is just. That's why I prefer a general crossing work because it's not that specific and pretty much is up to God/The Universe, as to how it manifests.