I hate seeing gum or other trash in urinals. It means that some poor maintenance person has to come and fish it out. Sure, people who clean public bathrooms wear gloves and generally clean up after people, but are you really so lazy and self centered that you are willing to add cleaning your trash out of the urinal to their list of unpleasant duties? Huh, urinal gum-spitting guy? The cleaner might have to change those cakes once a week, but you really want him to have to stick his hand in there today, don't ya?
Almost as bad are people who piss on toilet seats. How hard is it to lift the lid you savages? Push the lid up with your foot if you're scared of bathroom cooties.