I'm a Bisaya--a person living in the Visayas Islands of Central Philippines--and my native language is Cebuano. The Philippine national language is Tagalog, with a prestige register called Filipino, and, as it was a compulsory language to learn in school, I am fluent in its technical use and its use in formal conversations. It's useful to a certain degree but not really with anything more than understanding televised national news and literature, and conversing with people in the parts of the country that use it as their native tongue.
Tagalog, although it is the national language, is not my second language but my third. All schools in the Philippines use English as a standard medium of instruction and all but two subjects--history and Filipino--are taught in the world's most imperialistic language, which is also the language of Philippine government and commerce. On that note, Tagalog isn't very useful to those who don't speak it as a native tongue. One might argue that because the Philippines has so many languages, it can be used as a uniting language for us and that if two people who speak different regional languages try to converse, they would use Tagalog. Nope. This is simply not true in my experience. Although it is a bit shameful to admit, if a Waray-Waray speaker and a Cebuano speaker were to have a conversation, they would likely use English rather than Tagalog.
Moreover, since I don't actively try to improve my use of Tagalog, I've been largely ignorant about it's non-formal use. Even though it was pummelled into me during my years in school, I only learned it academically. Until fairly recently, I have only ever used formal and grammatically correct Tagalog. I didn't become street smart with the language until about 4 years ago. If you speak Spanish, imagine me speaking to you in the Usted Form with a Castilian accent while walking around the slums of Bogota. Or if you're an English speaker, imagine me speaking to you with the British Received Pronunciation while drinking Guinness in a small pub in Kilcullen. Yeah. Kinda like that.
Anyway, not actually using Tagalog on a regular basis, it took quite some time for me to learn bits and pieces of the language that are apparently really necessary if you want to survive in a place that uses it. Among them are the following:
a.) When someone says, "Wow, ang dami mong alam," [Eng: Wow, you know a lot] they're not giving you a compliment. No matter how deadpan the face of the one saying it is or how nicely it's expressed, it's actually just a sarcastic way of telling you to shut the fudge up.
Someone used this on me after I explained the difference between bisexuality and homosexuality--prompted by her assertion that bisexuality is just homosexuality in disguise. I thanked her after hearing it and went on about the principles of addressing cisgender people and how to be avoid being offensive. She repeated what she said. (i.e. "Ang dami mo talagang alam." [Eng: You really know a lot.]) I thanked her again and she left. Shortly after, a friend, who was also present in that conversation, pointed out that she was actually being sarcastic. It only hit me then why her grin was too darn big. She must have thought I was an idiot.
b.) Po, [a word used to express respect to an elder or "superior"; no direct English translation] is almost absolutely compulsory.
I was never told this in school. It took a confrontation for me to learn this. Someone approached me after a forum and said my speech was really rude because I didn't use the word po after each sentence when addressing a Roman Catholic priest. Right! That didn't help the guy's cause. From that day on, I resolved never to use the word with anyone who would expect to hear it. I am not superior to anyone and nobody is my superior so I will not address anybody as such unless they are really, really kind people and I want to make them feel good! I refuse to be another brick on a pedestal that boosts anyone's ego. The most I would do is say things nicely and gently but I'm not going to use a word that would make you feel like you're above me. You're not.
We Bisaya are generally nice and respectful people but we just express respect by saying things gently, which can be done universally with anyone and everyone. In our language, which is not mutually intelligible with Tagalog, we don't have a separate word that elevates a person's status in a conversation and I like that about my native tongue. Sorry, I'm not sorry.
c.) If you do not know someone very well, or if someone is supposedly socially "superior" to you, it is rude to refer to them in the second person singular. Instead you should refer to them in the second person plural or even third person plural. For example: "Saan ka pupunta?" [Eng: Where are you going?] should be expressed as "Saan po sila pupunta?" [Eng: "Where are they going?"; with po in its appropriate place]. Again with po.
d.) The word tarantado actually means "stupid." In both my language and in Tagalog, the word taranta (tarantar if expressed appropriately in Cebuano) means "to panic," so I thought adding a "do" after it, like you do with most verbs to turn them into adjectives--a Filipino adaptation of a Spanish grammar rule--would just make it mean "a panicky person." Nope. Apparently, it means you're stupid if someone calls you tarantado. An internet Tagalog-English dictionary translates the word as "flustered." Wrong. It really means stupid. Try being in a street in rural Manila and calling someone that and you're almost sure to get a black eye.
I used it the wrong way on a Tagalog colleague once, telling her, "Masyado ka kasing tarantado eh," after she got rejected from an audition to a singing contest. I thought I was saying "Because you're very panicky," when I was actually saying "Because you're very stupid." No wonder she cussed at me and didn't speak to me for over a month after that. Sorry, we didn't learn such words in school. I'm glad I didn't use that word too much.