The art where ones testicle is extremely larger then the other. In this case, BTB will stand for Big Tumour-like Bollock.
The other meaning for BTB is an attribution to ones extreme lies- pyschodynamically an impulsive need to lie. Related to the former meaning through the use of bollock, which here will mean a load of rubbish or a lie instead of testicle.
Hey, thats one BTB you got there!
Hey, thats a load of BTB and you know it is. You dont play Rugby for, Wales, England, Fiji and Germany Fuckface!