The definition isn't for sure, but the word "donkelope" is used as an insult such as: "you dummy!" this word can also be related to "donkey" or "antelope".
A dönkel is a person who always falls in love with the new partner on the first date. This phenomenon is also called dönkel-effect. An average dönkel experiences this effect about four times a year.
Friend: "How was your first date?"
Dönkel: "It was amazing, it was love at firstsight!"
Friend: "Oh, the dönkel-effect again."