I'm not going to greet my girlfriend when she comes home from work today.
Why don't you want to say hi to her?
I just don't feel like it.
It's expected that couples will say hello to each other when they see one another. If you can't even muster the energy to say hi to her, things may just get worse for the relationship in the future.
If she wants a greeting that badly, she can come find me.
If you're not even willing to show this small gesture of kindness to your girlfriend, there may be larger issues in your relationship. Saying "hello" to her would only take a couple seconds out of your day, but would make her smile and feel good. If you can't do that, you really need to re-examine how you feel about the relationship.