Venmo etiquette is an underrated brand-new etiquette in the digital age. Anybody can request money from anybody unprompted and unannounced. For some, this is an incredibly convenient way to pay somebody back without cash or clunky old PayPal. However, it's easy to push this resource to its limits. There is no reason to be requesting your friends and loved ones $2 for anything. Before smartphones, people would pay for each other all the time and know that the other person would pay for them the next time. These days, nobody trusts each other anymore. That's how you get Venmo requests for one bottle of Diet Dr. Pepper.
Roommates can go a little hog wild with Venmo requests for silly things. You don't need to pay 50 cents because you used your roommate's mustard one time. You especially don't need to Venmo request your roommate $4 for eating a cookie made with her ingredients.