Say I want to make the MC a bit of an ass at the beginning (to start his character development), personally how would you make sure that the reader isn't annoyed by the MC's assness and leave at the beginning without reading through and seeing the character development
Coincidentally, I've just finished reading "The Naughtiest Girl in the School" by Enid Blyton (Yes I raid my children's bookshelves and/or the children's section at the library.
), and while it's a children's book, the basic principle is the same and it illustrates some answers to your question.
The MC in this book is a spoiled, overindulged brat who gets sent to a boarding school by her parents after yet another governess resigns due to her shockingly bad behaviour and attitude.
How does Blyton make the reader sympathetic to the MC in spite of her being an insufferable brat? (and I had sympathy for the character right from the very beginning) - I'd say there are a few ways she does this:
1. She portrays the MC's genuine emotions about the prospect of being sent to boarding school and how she feels when she gets there, i.e. fear; not wanting to be away from her parents, her pony or her pets; homesickness when she gets there; loneliness when the other kids don't want to be friends with her because she's rude, won't share her things, etc.
2. It's clear that underneath the bratty exterior, there's a kindhearted, caring little girl trying to get out, just that she's been spoiled and indulged too much so she finds it hard to understand the effect her behaviour has on others, beyond trying to manipulate people to get her own way. But there are also things she does and thinks that shows she does care about other people, even if she doesn't show it much.
3. Her motivations for misbehaving are clear - she thinks if she's really naughty she'll get expelled and sent back to her parents. Why? Because she's afraid to be away from her parents and she's homesick (ties in with point 1, above).
4. Her naughty antics are funny - the kinds of things better behaved children might think of doing, but never dare to. But no real harm is intended. She's not actually trying to hurt people.
5. The other kids and teachers give as good as they get, i.e. people stand up to her. This doesn't instantly make her good, but it highlights her vulnerable side.
Due to the age that this is aimed at, it's rather simplistic compared to books aimed at older children, teens and adults, yet I think that it encapsulates what you need to do to create a character that's a complete arsehole yet one that readers will sympathise with. Just translate the above into your character's situation, only be more subtle about it and make it more complex.