You shouldn't aim for "Worst flavour". Maybe "no flavour"? The flavour is 90% of what keeps people vaping IMO, and thats where the success comes from. Being able to stick with it for a long period of time. I can see myself doing this for a few years, then stopping gradually with relative ease. I already sometimes forget to vape until 2-3pm and i used to be a 1pack a day smoker. So this is my personal life line to staying in good health. All that is my opinion though
If you want no flavor, just ask for a no flavor base with your desired nicotine level and a little bit "PG"ish, but I don't recommend that. I don't often smoke fruity flavours and all tobaccos were "sweet". I go for tart, bitter, heavy flavours. Certain tobacco blends are known for being less fruity. If you have a specific goal and flavour profile you prefer maybe an experienced mixer someone can help!
If you really just want a crap flavour, some youtube reviewers say one of the RYs (1-4) tastes like socks and camel spit.
Plain PG/VG+Nic should suffice if you're really not interested in flavour, but i'd be surprised if that helped you quit.