Be careful with the bet, there are differing opinions on this....
Trenbolone can induce progesterone gyno. Reports seem to start to happen at 150gm/eod. I'm not hearing reports at lower dosages. Also, some people seem more prone to it than others.
Bill Roberts strongly believes that it is not progestogenic and makes an interesting argument. But there is evidence otherwise, both in studies and user reports. It's probably happening through a less obvious channel.
I don't have a link handy for this, this was covered recently on the Fina board and there was a pointer to a study as I recall.