Have your partner give you a blowjob and catch the entire load but not swallow. Instead, have them give you a Cum Kiss or Cum Swap to split the load between you both. Go about your day keeping the loads in both your mouths. The first to swallow, loses.
You can make it more exciting and bet something like the loser gets fucked in the ass. (If a female wins, she would be using a strap-on for him.)