wet dream is when your body needs to excrete sperm that has been
stored in your body.
Usually, this happens with dreams of sexual nature. But its also
common for guys to have "wet dreams" without dreaming anything, you
just notice something in ur underwear when u wake up the next
morning.
For those who really want wet dreams, simple, don't pcc/ejeculate
for at least 3 to 4 weeks. I am pretty sure u will have ur dreams
within that time frame. 
