There are dress codes for yoga, without which it becomes difficult to practice yoga. Sometimes you can invite some problems also. For boys and men wearing underpants(below shorts) is a ‘must’, otherwise they will face problems. The bottom-line is that ‘never wear any dress which are very tight and create obstacles in free movement of limbs hindering blood circulation. But once again I repeat that wearing underpants(which is tight) is a ‘necessity’.