@NewEnglandSkier I did see this post a while back, but honestly I have never really had this problem with clothes/rashguards/ swimsuits etc. I did a quick google search and found some help that suggests either scraping cold or letting warm up in the sun ...similar I guess to getting candle wax off a table cloth.
I think Gloria is correct in that it sounds like they were using a "cold water" wax on a warm day...... base coat and tropical/ warm wax is much "harder" than cold water wax which is "softer." If the water is warm, you need a harder wax or it will get slippery and melt.
I agree that if you use a cold or cool water wax on your board an apply liberally, sometimes a bit will stick on your wetsuit (white butt) but thats if your only using really soft wax. Honestly I've surfed very warm and very cold water any the only time I've had any residue on any fabric is the cold water wax on a wet suit which as Gloria stated wears a way after a short time.
Now for some reason, I find wax in the oddest places on my wood floors -- granted, we tend to strip the wax outside and sometimes wax up in the living room, but if I have a mark on the floor its usually surf wax! It also sticks on leather car seats..... a good reason to use a day bag if you drive w/ your board.
We as a family have been collecting wax for around 2 years... I'll send a picture of the ball if I get a chance... really you should strip your board and rewax if it starts to look dirty or the "texture" changes.... (too many unknown chemicals in the ocean change the structure of the wax)
So that leads to the question of ROUND or SQUARE? what type of wax person will you be?
@Jilly is round or "sexwax" user (so is my husband)
@Gloria is a Square or "sticky bumps" user as I am.
It all boils down to preference, and really there are marked differences I find in even within the brands, as I use the Original sticky bumps, but my daughter uses the Munkey which is sticker -- If the place you rented a board from used the Munkey Cool/Cold water wax when the water was over 70 degrees, I would understand why it was stuck in your clothes!!!!!!
Sorry I can't really help, but I think if you google surf wax removal you will find some tips that may work...... Good luck getting it out!