ALWAYS have a piddle before takeoff, you never know when the next one will be. But being caught inside a cloud in very cold temps, half-way through the outbound leg of a VOR with a dopey student taking his time, was not a pleasant experience.
He wondered why, instead of the pre-briefed missed approach, we did an auto to the far corner of the field, where I leaped out and broke the seal. On the back of the skid. The intercom lead didn't let me go any further back than that.