Revision #4. Cold and Sour Strawberry Watermelon. Not too sweet but definitely a pronounced sour tangy watermelon on the inhale with a 'just right' icy kick of strawberries on the way out.
For lack of a better name, I'll just sound like an idiot and call it Strawwdurrmelon until I come up with something.
Similar to omg WTF Ice, Modus Molly, 100 Proof Sour Nectar & Apothecary Elixir No. 01. If any of these are familiar to you, you'll love this.

TPA Strawberry/Strawberry Ripe + OOO Strawberry Sour Belts
The classic strawberry mixture with a tangy twist. The combination tastes like a strawberry with some under-ripened bits near the stem creating the sour fruit profile without needing to add too much citrus.
TPA Watermelon Candy
It's a very strong flavor and easily overpowers the rest if not kept in balance. Similar to the sweet candy center of a watermelon Warhead after the sour is consumed, I thought this would be a perfect match for a sour strawberry.
FA Lemon Sicily & FA Fuji Apple
Combined these two flavors help the other fruits pop. The lemon might be attributing to the sour effect.
INW Cactus, TPA Koolada, FW Menthol:
The not-so-secret sauce! Combined together create a very wet but not too icy vape.
TPA Sour
OOO Strawberry Sour Belts didn't have quite enough pucker on it's own and this picked up the slack nicely. Be careful as this can mute your flavors if over-used.

--Credit to Daniel Store from the DIYorDIE Mixers Collective for the original theory-recipe--

You can get a similar (But certainly not the same sour kick) flavor in lieu of OOO Strawberry Sour Straws by increasing TFA Sour to .4%, TFA Strawberry & TFA Strawberry Ripe to 2%.
To make it more candy-like without needing sweetener, increase Watermelon Candy to 3%
I recommend 75/25 VG/PG Ratio but 70/30 works fine too.
It's fine after just a day of steeping but really shines after day 3.
ICEE needs to get in on this asap. I want to drink it but I'll die.

Steal this recipe. You're free to share it, sell it, give it to your friends and tell them you made it, I don't care.