Sombody has crossed you or did something you didn't like. You have this desire to effect revenge, to balance the universe, to set things right and give them a bit of their own medicine. It's a natural feeling. Plus getting revenge feels good!
I'd like to submit the following for you to think about.
Karma is the law of cause and effect. While many people think about karma as a direct response to an action, that's not exactly how it works. When somebody lies, they contribute to the conditions that somebody will lie to them. They create the conditions where they will be caught lying. Even if these things happen, there may not be any noticeable effect. However each action causes a reaction. And the sum of these reactions over time will cause a degradation in their happiness. So in essence a person will get back what they put out even if it takes some time.
Now, back to revenge!
If a person does something mean, I submit that before taking revenge (which is a bad action that will contribute to your unhappiness), you think about whether or not you're the right person to effect Karma's balance.
As martial artists, we have a set of skills that can be used to stop harmful actions and we are familiar with forms of violence (mental and physical). However, when we use these skills, we also contribute to our unhappiness. So we must be thoughtful. Does the situation warrant the unhappiness that this action we're considering contributes to. Most often the answer is no.
"Am I the right person to effect the karma" is an interesting (if overly ego centric question). Consider that some person who has been putting out unhappy actions will likely meet another person who consistently puts out unhappy actions. When these two meet, there is a good chance for one or both of them to take an action that will result in the revenge you were seeking. Somebody else will get your revenge for you. How efficient! You can rest assured, if necessary, that the universe will ultimately balance out.
There's an expression that rotten fruits will fall by themselves. All you have to do is wait and let nature take its course, no need for intervention.
Ving tsun kung fu is a training ground for life. When we train in ving tsun kung fu and practice a drill with our partner, we can experience a microcosm of life. Try to act with your partner in a way that they enjoy using reasonable techniques and a kind heart. Then act in a way they don't enjoy using unreasonable techniques and malice. I think you know what will happen; and it will happen quickly. In this case Karma does not have longer than usual wait times.
So the next time somebody does something you don't like, you can just walk on happily knowing the universe has got your back. This thinking will also help breach that gateless gate you didn't know you were trying to get through.
Once on the other side of that gate, you will recognize that the person who deserves revenge is suffering and is acting out because of it. They need help, not revenge. And you know the universe is lining up a whammy, which will compound their unhappiness and make them act out more. That need even more help and compassion to deal with their impending crash.
I therefore recommend holding off on that revenge and trying to understand what would cause them to act in such a way. Have patience and compassion for their situation and treat them kindly instead. You will find yourself happier and given enough patience and kindness may even lead them to find happiness too.