For me it's because my mouth tastes terrible and I want that gone asap

Because that is better for your teeth. Talk to your dentist about it. https://www.healthline.com/health/should-you-brush-your-teeth-before-or-after-breakfast

I don't eat breakfast.

Healthier on the enamel, tho I don't do it (and most of the reason you brush is to get off the built up stuff from overnight, not clean off breakfast)

If you smell your breath first thing in the morning it stinks. This is a sign of bacterial overgrowth. During the day, the biggest barrier to this is natural saliva production and agitation through movement of the mouth. These things are drastically reduced while you sleep and thus leads to a build up of bacteria. This is why it is advised that you brush your teeth after waking.

Technically, it is also advised that you brush your teeth after each meal but that is not practical for most.

Because acid in your breakfast can damage your the enamel of your teeth when you brush. (I'm not a dentist but that's what I found from most health-related websites.)

https://www.healthline.com/health/should-you-brush-your-teeth-before-or-after-breakfast

Not a dentist, but the reason dentists gave me for doing it in that order is that bacteria and plaque build up a lot while you sleep, since your teeth are just kind of sitting there doing nothing. So I guess waiting until after breakfast is just an unnecessary delay.

The health related reasons others gave are interesting, but my reasoning is this pretty simple: On normal weekdays I don't really have breakfast, so brushing my teeth as one if the first things makes sense. On weekends I like to have breakfast with my family so I'd like to get rid of morning breath before I talk to people.

Build up of bacteria at noght means that if you eat in the morning before brushing there will be more bacteria to break down the food into acid which will break down your teeth.

Ideal is to brush first but also brush after each meal*

*as long as the acidity in your mouth is 5.5pH or less your teeth are being broken down by the acid (which means that brushing would be scrubing them with acid and making it worse) in which case you should wait until your spit (which is a buffer solution) returns your pH to normal. Since most foods are acidic the recommendation is to wait 30i mnutes after eating and then brush. Or you can eat suger free gum right after a meal, this will trick your brain to produce more spit which will return the normal pH faster.

My personal system is like so:

Wake up

Use dental jet floss (water floss)

Brush teeth

After any foods eaten chew gum for 10-30 minutes

Floss

Dental jet (if at home)

If I'm at home and have 30 minutes to wait between mouthwash and brushing then I use mouthwash, wait 30 min then brush, if not then just brushing and if I'm not at home then just mouthwash.

Repeat for as many things as I eat that day.

Before bed:

Floss

Dental jet

Mouthwash

Wait 30 min

Brush

huh, TIL brushing before is apparently better

I go 1, 3, 2 because it was easier for me to form the habit that way. I don't always have time for breakfast in the morning, so I anchor it to 1 instead of 2

You should wait about 30min after eating something acidic: https://www.cuimc.columbia.edu/news/brushing-immediately-after-meals-you-may-want-wait . Some people don't have time to wait. Myself I don't eat breakfast at home, I brush my teeth, go to work and eat when I arrive.

you know how your teeth feel smooth after you brush? that smoothness helps things like coffee not stick to them, in turn helps avoid stains

brushing before coffee is legit the thing to do

For me it's a habit formed as a young boy because my uncle taught me that while I'm asleep Satan shits in my mouth and if you eat before brushing your teeth you're eating Satan shit. True story.

I dunno, if I gag while brushing and I've recently eaten, I'll throw up. Also I don't usually eat for several hours after waking up, it's coffee then late lunch then dinner, so waiting to brush doesn't make a lot of sense.

Also, I get toothpaste stains on my good clothes if I brush after breakfast

Because you have to wait 30 minutes after eating before you brush your teeth or you damage them. I don't have that time.

So I rather brush first, then shower, then make breakfast.

Having to wear a removable retainer at night means I wake up with congealed spit stuck to my gums and teeth. The visceral ick of swallowing that is indescribable, so I will brush my teeth first thing, then eat breakfast.

Cuz my mouth and throat feel disgusting in the morning. Eating or drinking right after brushing doesn't bother me either.

The fluoride in toothpaste creates fluorapatite in your teeth which is harder than your regular enamel and more resistant to acids.

I don't usually eat breakfast and I try to be vigilant about brushing my teeth, so doing it first thing is pretty natural for me.

My dilemma is usually closer to whether I brush my teeth before or after taking a shower.