How come you give your best when don't have a good relationship with your boss?

Giving your best and good relationship are both important:

First try to understand your boss either his/her criticism is focused towards you only or same for all. I believe if he/she is stayed in company then he must be good resource for company. Try to understand and facilitate him the way he proceeds/likes in his team's assignments. Take as a learning for you and try to manage boss. Initially it looks difficult but after some duration he might be Ok to you if he is a professional and concerned with outputs only.

It is right you cannot give your best becuase at the end your boss is the one who will rate it as best or worst. 

Take it as challenge in a positive way. I hope it will work...

Best Wishes!

To better your own life and not loose track of who you really are and what you belive in.

For me, the answer is your career! You have a career to protect, which I bet you wouldn't want a bad boss to ruin for you. Remaining focussed and professional is very necessary. You will be emotionally troubled most times, no doubt! But, tolerating such bad bosses is the only way out. It could be frustrating, but one has got to just remain professional and focussed.

I once had a boss who wasn't so fantastic, but I tolerated him till I was able to get another job, and I moved on, much to his chagrin.

I give my best to my customers because they are the reason I have a job. Looking after their needs and keeping them happy is my job, so that they can come back again and support our Company. However the relationship is with my boss must not affect the way I do my job, I must always give the best service I can, show a positive image of the Company and a united front and the spirit of teamwork infront of the customers.

that is when intrinsic motivation is at its peak

Knowing the nature of the person you will be working on is essential to your success. Although this is not always something you can control, you can take note of some references to the manager's personality and behavior during interviews in particular.

A creative entrepreneur or manager, for example, will constantly challenge you, give you new growth opportunities, but will not necessarily manage you effectively, and you will have to do the hard work yourself.

You should have thick skin and always ignore him but ensure that you wont cause any problem. The irony is if u can stay with horrible boss its a complete win. 

First of all, l see my boss as someone that l'll be intouch with for the rest of my life. Sure, l may work for this person–probably for a short time, maybe a year or two–but l'll be building a relationship for the bigger picture. in order to have this, first l'll have to be loyal to my boss, l'll try not to keep secrets(work-related) from him. Secondly l'll have to empower my boss, by making him or her look good and this mostly will come to the clients by speaking good of my boss and how much good results one can get by working with us. l'll have to think about what l can do to make my boss look great.

l think the rest of the things will fall in good place once there is good comunication between my boss and l.

To concentrate on your work/job