This can include hormonal problems as well as testicular cancer, infection, or blockages. Therefore, it is important that the urologist or male fertility specialist prior to proceeding with in vitro fertilization evaluate the male partner. Recently several studies have addressed the effects of smoking on male fertility. There is some very good evidence that smoking can have an adverse effect on sperm count, motility, and function. It is always a good idea to quit smoking, particularly when trying to conceive.
Alcohol is slightly more controversial.
It can be, but this is a rare finding. However, the most common type of cancer in men of reproductive age is testicular cancer. This would be discovered during the evaluation of the man. I've read that bike-riders have to be careful what kind of seat they use as to not damage the testicles. The best evidence regarding bicycle seats pertains to erection, not fertility.