Typically we use "dude" to our friends. It is more commonly used by men than woman. However, if a woman wants to show that she is "one of the guys" she will often use "dude" to her male friends. (I have done this many times before). I wouldn't say "dude" to someone I am romantically interested in. It kinda makes things feel really neutral. As for its usage, if you are familiar with the slang word "man" you can use "dude" interchangeably for it. "dude" and "man" don't really have a very clear meaning, as they are both used in a lot of different situations, and their use is very flexible. But for a general rule, you can use "dude" or "man" to add emphasis to a sentence. For example: "Dude, I really need a vacation!" — Here "dude" is just adding emphasis. You can also use "dude" to get a friends attention. For example: Your friend is looking in a different direction than you, but you want to show him something: You: "Yo, dude, look at this! Its so awesome!" Your friend: "Haha, man, that IS awesome!" You can also use "dude" as a term of endearment, for example: "See ya later, dude." This is just a friendly way to say goodbye to a friend. "You're the best, dude" This is a friendly way to tell your friend that you appreciate them In both these examples "dude" is taking the place of your friend's name. I hope that helped a little! :D

In my opinion, the term "dude" is a little outdated. If you did use it, you would never say it to your boyfriend/girlfriend. People I know say "hey man," instead, if you're talking to a man (girls can say this to boys, or men to men, but you would never say this to your boyfriend.)

The word "dude" is used by boys or men, who are using a casual slang for "guy", "man" or "boy". It would be used by friends. It is not often heard, and is said among "pals". Boyfriends and girlfriends do not use this word among each other....it is not a romantic word. It is not used in formal speech, nor refined "polished" people. Yes, two buddies could call each other "dude".

You can feel like you are a friend when with your special someone and say dude if you are surprised by something. This is not a thing that would happen consciously because dude is meant for men. It can be an exclamation though. This is how it would be used. "dude!" did you see that bird grab that butterfly? Besides that that, it is for guys. Dude, I heard a bird grabbed a butterfly.