I do feel sorry for you OP!
People are being way mean, but it is also very funny. I hope you can also see the funny side and you can take this a bit on the chin! I would be defending you if we were all in one room but I would be laughing at what people were saying at the same time! So yeah, chin up. I hope you can withstand some of the banter.
Ok, so to the actual question!
You're right I don't wash my undies at a 30 degree wash. I tend to do a knickers, socks, tights, pyjamas, husband pants, socks altogether as one wash on a 40 and I add dettol laundry cleanser, more because of my husbands socks! Haha.
You really don't need to separate them while they wait to be washed - honestly. It all comes out clean. Afterall you don't eat off your clothes, so there's no reason it has to be sterile. The detergent (like soap) will get the germs out. You don't wash your hands at 60 degrees and you do eat with them, you know? Honestly these days we don't need to wash anything at high temperatures because detergent is so much better than it used to be.
Although I was grossed out at the poster who said she washed her teatowels with everything else! Ugh! I do, do a separate wash for tea towels, cleaning clothes etc and I add a bit of zoflora to that wash.
If you're still a bit grossed by the thought of washing some things together at a 40degree wash - you could get some napisan. That is for reusable nappies, and that really is to make it as sterile as possible because it's for babies. It will kill the germs! You just add it to your usual wash.
If you really want to separate and worried about builders - suggest getting one of those cheap sports bags, you know like the old gym bags we used to have as a kids? With a rope style pullie thing. They scrunch right down to nothing. You could put your undies in there and just stick that bag into to the washing basket.