Abstract: A spill-proof drinking mug for drinking using either left or right hands of the user in which a base part serving as a container for the liquid is provided with a shape designed to fit within conventional cup holders of vans and RV's as well as cup-holding attachment for automobiles, and which has a threaded top opening. A screw-on cap with a handle sealingly mates with the top opening of the vessel, and has a pair of drinking openings at opposite sides of the handle. One opening is used for drinking and the other serves as a vent. A spring-loaded valve is mounted on the cap and is operable by the thumb of the hand holding the handle to simultaneously displace the valve out of both openings.