When you make plans with someone to do something but then after you made the plans you cancel them and do something else with a different person. Some people think ditching is when you invite someone somewhere and they can't come but it's not.
To leave a person, place, or group of people suddenly and unexpectedly to hang out with someone else, somewhere else, or to go to another large gathering.
To leave someone or a group of people suddenly, often without their knowledge, making it all the more comical. Whoever said it comes from the German word dich is and idiot because dich means "you".
1) when someone leaves a group/party to go to another party or group of people
2)When someone says no to 1 person but yes to another person to a party or hanging out on the same day
3) forgetting about something purposefully