lul (dick)
sukkel (stupid)
idioot (idiot)
Insults that start with the letter d:daffydensederangeddimwitteddisgustingdishonestdopeydowdydrunkdulldysfunctional
Pansy
insane
Quitter!
rectum sucker
Asinine is an insult. It begins with the letter a.
Me cago en tu madre!
There are many websites and blogs that have lists of insults including Buzz Feed, which features Shakespearean insults to Wikipedia, which has a list of ethnic insults.
Surrats Sewer Rats Rats
insults starting with the letter L
Couillon - fool, idiot
Rude people are an excellent source of insults. Also Chavs