are you serious??
Yes, I heard that.
Maybe it's a way for us to realize that giving someone a baddua can backfire. At the same time, if you say good things towards a person, you have the angels saying "same upon you" to that as well.
Re: what would you do if you find out someone is planning
^ but what if you are wrong/hurt by this person? as zobia has mentioned,and u say bad dua out of anger 
are you serious??
She's right. The dua that you make for your Muslim brother/sister in their absence (ghair haziri) is accepted or qabooled the fastest. And when you make a good dua for a person.....the angle say "same for you"......and if you wish ill for someone the angels do the same.
However, I do wish that Allah teaches some people a lesson when they don't shape up. I can understand making mistakes by accident....or losing your cool a few times.....and then apologizing for it. But for people who continue to hurt others without showing any remorse or making amends (even a verbal apology) and only display pride......I do hope that Allah teaches a lesson to stop them in their tracks....because it's not good for so many others to suffer because of them.
evil against you? wishing bad luck for you? bewitching you? astray you? or anything that can ruin your life (which some how give them comfort)
how far can you go? will you also do the same with them? or will you also at least wish the same for them?
u cant do anything..theres nothing u can do..if u wish bad for them or try to do something to harm them it will backfire so better to just recite specific surahs nd work on maintaining ur peace of mind..n yoga is really good for relieving anxiety..works really well for me at least
Re: what would you do if you find out someone is planning
do what raaaabert would do 