1. of, showing, or characterized by deep thought.
2. of grave or somber disposition, character, or manner: a serious occasion; a serious man.
3. being in earnest; sincere; not trifling: His interest was serious.
4. requiring thought, concentration, or application: serious reading; a serious task.
5. weighty or important: a serious book; Marriage is a serious matter.
Being serious is usually associated with being solemn or not laughing a lot or something like in definition 2. But to be serious about something means you take do not take it lightly, that you have given it thought.
I call myself a very serious person. A number of people disagree with about this. They point to my hilarity when I eat ice-cream at 10pm, to the way I like to think that elevators are magic, to the way I wave my arms around and sing in the kitchen, and to the way that I laugh and smile all the time. So yes, it is true I do very silly things and you cannot use the second definition of serious to describe me.
But I am truly a serious person if you mean that I take deep thought about things. I am deadly serious about my walk with Christ, about my aim to bring joy to others. So I pretend to be a clown when someone is sad. I take care in the food I cook even if I am singing. Actually I sing because I am having so much fun taking seriously the food I am cooking. And when I decide to eat ice-cream at 10pm, I seriously consider the consequences and whether I will act appropriately in the situation at hand if I allow myself to do such a thing.
Also I am slow to get jokes and puns and I am not quick at thinking them out myself. If I say a joke, it is usually by accident and I am the most surprised. Because I always try to say exactly what I mean and to answer as fully and truthfully as possible (this is harder than it seems because my answers are never simple to explain, so I usually end up just not explaining to save all the time I would need and so the person I would be explaining to would not get bored. See? a long explanation in parentheses for example). Because I am like this, I tend to take what other people tell me as true and therefore I don't always get the jokes and puns and stuff. But since starting work, I have learned to think twice before saying things because some things can be taken in a dirty way, so I have to consider what I am saying even more. But my friends do not think these ways (or at least, they have learned not to take it that way if I say something) so I don't believe they think I am a quiet person.
Ah the only thing I am not serious about, I think, is my manga reading. Except that I call myself an otaku (Japanese word for someone with a nerdy obsession for something, American for someone obsessed with Japanese culture). But I read very light happy things. And I use it to take a break or as relaxation. That is why I think I do not take it so seriously.
So I guess maybe it's just that I think too much...
Also, why am I posting around 2:30 in the morning? Ah, I have been reading manga and stayed up too late. It is definitely time for bed.