Asinine is an insult. It begins with the letter a.
Insults that start with the letter d:daffydensederangeddimwitteddisgustingdishonestdopeydowdydrunkdulldysfunctional
insane
Vent-head.
Pansy
Quitter!
rectum sucker
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.
Get a life! Get lost! Go pound salt!
Here are some insults that start with the letter W: weakling wuss weirdo woman witch Why are you so fat? Where did you get that ugly mask? When did you have time to get a PhD in stupidity?
Surrats Sewer Rats Rats
insults starting with the letter L