Gather 'round, children, and I'll tell you a tale of long ago, when
coffee cup lids were designed to prevent coffee from spilling.
One day, the evil Grand Vizier whispered in the Sultan's ear: "Sire,
coffee cup lids are badly designed. When in place, they prevent
people from drinking coffee."
Sultan was distressed to hear of this. He himself only drank
from fine china, but he cared deeply for the welfare of his
subjects. The Masters of the Guild of Coffee Cup Lid
Manufacturers were summoned, and, after the customary
obeisances, a proclamation was read: "Henceforth, all coffee cup
lids shall be pierced with a hole, so that coffee may be drunk
freely, without removing the lid."
Coffee consumption rose, and with it punctuality and productivity.
GNP increased, and with it, the tax base. The Sultan Saw that It
Was Good. Anyone carrying a cup of coffee had to move
cautiously, to avoid splashing through the hole. The Paper Towel
Manufacturers, Dry Cleaners, and Upholsterers guilds paid the
agreed-upon bribe to the Grand Vizier.
In short, old-style lids (first link) had no hole, and were removed
before drinking; new-style lids (second link) are designed for
drinking with the lid in place, and have a hole. This is supposed
to give the best of both worlds -- drinking without spilling, but it
doesn't: when I walk briskly holding such a cup, coffee splashes
through the hole.
I propose the addition of a baffle underneath the hole in the
plastic coffee cup lid, to prevent splashing when the cup is jostled,
while permitting a gentler pouring action by tilting the cup.
Picture a flat, horizontal bit projecting inward from the lid
circumference, a few mm beneath the hole.
An easier-to-manufacture solution is shown in the third link -- yet
this is not widely used . (That's my impression, and a Google
Image search on "coffee cup lid" (no quotes) supports this.) I
believe the reason is that the lid in the third link isn't as
comfortable to drink from.