The ways that I speak that fall under the "serious" category are usually more snide and straightforward. I say whatever comes to mind without holding back; it's also not completely serious, as I tell jokes with it. (It's just named that way for the sake of contrast). I also use more sophisticated word choice (and sometimes a more British-sounding or old-timey accent): "but of course," "insinuating," "exemplify," etc. It's very structured; I speak grammatically correct sentences with very few colloquialisms. I use this whenever I'm with pretty close friends, as I can be a bit freer with my harsh remarks than I can with mere acquaintances. The sophisticated word choice is just me semi-consciously trying to make myself sound smarter (but I also like how those words sound). This is the form I use the most throughout my daily life, as I often encounter moments where I need to be serious; I usually default to this if I'm not specifically trying to use the other English often.
Those are the two "Englishes" that most people can understand... so what of the third one? The third one is more of a "mod" or an "add-on" so to speak; in fact, it's not English. It's a combination of random Chinese, Taiwanese, and Japanese phrases that express what I want to say better than I could in English. Obviously, by themselves, most people would be clueless as to what I am saying; however, I use them in situations where it makes sense and only context clues are needed to understand them. For example, if someone asks me a question that I couldn't quite comprehend, I often use the Chinese/Taiwanese word for "what" with a look on my face that people usually have when they say "Huh?" or the like. People usually pick up that I'm confused about what they've said, even if they don't fully understand exactly what I said. I mostly use this, alongside normal Chinese, whenever I'm with Chinese speakers. It's a simple divide with some overlapping words: I use mainly Chinese with people who mainly speak Chinese, using a little English for words that are better expressed in English (like "anyway" and some obscure nouns), and I use mainly English with English-speaking people with the exceptions I mentioned above. (I don't speak just Japanese with anybody; they're just a few words I picked up from my sister and other places). It's just easier for the involved parties to understand what I'm saying. If anyone wants to hear my super enthusiastic voice say some of these exceptions, I recorded them for your listening pleasure.
By using a more "serious" form of English, I don a sarcastic and smart personality. I am quick to retort, and I play the straightman when it comes to jokes. I also flaunt my knowledge; I let people know that I know a lot. As such, whenever I use this English, people often tell me that I always "roast" people and say I am smart. It boosts my ego to do these sorts of things, but it can get pretty sinister if I go too far with it. I balance it out with my "not serious" form of English. When I use this form, I sound much more easygoing and laid back. I'm less tense; I tend to seem happier and laugh more speaking this English. It is definitely a lot funnier for me; I like messing with people by acting dumb. Therefore, by seeming like I'm much more stupid than I actually am, I can be the trickster archetype that I love in various forms of media; I manipulate people and make them do things they would not do normally. They have to go out of their way to explain things, or I mess with their thought process to make them think differently. With my last English, I create a worldly persona. I emphasize that I'm bilingual- that I can speak multiple languages. I can switch freely between languages, and people view me as knowledgeable instead of just smart. Whenever I'm in public with my parents, I use Chinese to (hide insults about the people around me and) reveal that I posses the ability to interchange between all my Englishes. I can change from the "carefully wrought grammatical phrases" (Tan 700) of my "serious" English to the extremely informal speech of my "not serious" English, and I can use them interchangeably with my other English that isn't really English. With these tools in hand (or mouth), I can get through any sort of situation that comes my way.