792. At the start of the adventure, as the PCs are traveling from City A to City B, have the PC's make CON checks every hour. Set the DC to 5 (so that most SHOULD make the first couple). This will work really well if all the PCs make their saves the first few times. Increase the DC by 1 after each check, so Hour 1 DC 5, Hour 2 DC 6, Hour 3 DC 7, etc. When one (or more PC's) fail, tell them 'You feel very uncofortable, like your bladder is going to explode at any moment.' Don't reveal that this is because, well, the PC had too much Ale and now needs to pee. This just may freak the Player out, thinking they have some disease which may kill them. The next hour, have the PC's who passed their save make CON checks. If they pass, rinse and repeat. If they fail, tell them the same info. For those that failed the previous hour, make another CON check, if they pass, tell them the pain is receeding and is bearable, but your bladder still feels like it might explode. If they fail the CON check, have them make a Will Save (same DC as the CON check). If they pass, all is good (heck, pass them a note that says 'Act normal for now' as mentioned above to really drive up the fear). If they fail their will save, say to the failed PC (who may think he is about to die), 'You feel a slight tickle of water run down your leg, when you realize its not water, but urine.'
793. Use ability checks/saving throws in other interesting ways, like above. Mix in a few that truely have dire consequences. Your PCs will never know if their checks are a matter of life or death, or wether they need to use the outhouse.