It would be easy to answer "how was your day" with one word such as "fine" or "okay." Men are very different in how they see their day as opposed to women.
"The brains of men and women, while similar in many ways, are more different than most scientists ever realized," says Larry Cahill, Ph.D. Men think in terms of things and results. Women think more in terms of emotions and desired outcomes.
"How was your day?"
I understand coming home from a day at work feeling tired and irritable. I understand you just want to get to your comfy chair (although you don't call it that), but do you understand you're at a crucial moment? "How was your day" is a gateway question; it is a gateway to conversation. Your wife is saying she'd like to talk to you. When you answer with a mono-syllabic word you're effectively shutting the gate, and, depending on how you answered, you might have slammed it shut.
When men are with their friends, they never talk about feelings, relationships or use sentences longer than four or five words. Dr. John Lund, therapist and author, suggests men "become impatient with inefficiency" to the point of finishing others' sentences so they want their answers short and sweet.
"Really. How was your day?"
Conversely, Jim Butcher suggests in his novel, Cold Days, women can have a conversation on five levels at the same time. "They follow the conversation that they're actually having, the conversation that is specifically being avoided, the tone being applied to the overt conversation, the buried conversation that is being covered only in subtext, and finally the other person's body language."
Understanding this helps you see how your answer of "fine" or "okay" is insulting. She is asking because she cares about you, and wants to help you deal with your stress. The way women deal with stress is to talk about it. Men don't often understand this. They're more interested in not thinking or talking about it. If you want good communication in your marriage, get over this.
Bonus points for texting
When your wife asks you about your day, you need to tell her how it went using examples. You need to tell her how you felt about those examples. It takes patience and practice. Something that helps is texting counts! If you don't want to spew forth at the end of the day then text along the way. This shows you are thinking of her and want to share things with her. You'll earn big points doing this.
There's one last thing that's even more important. After you've answered her question appropriately, you need to ask her about her day and listen, just listen. You can comment in appropriate places but understand if she is talking about a problem she doesn't necessarily need you to fix it but just listen and comfort, laugh, or celebrate with her. Use these tips and see how much better your communication is between you and your spouse. She'll wonder what happened but I won't tell if you won't.