If you're angry, count to ten. If you're really angry, count to a hundred.
Literal
Belly [subject-が] angry-stood-[if-たら] ten count. More belly [subject-が] angry-stood-[if-たら] hundred count.
A famous quote (attributed to Thomas Jefferson). Uses ~たら conditional twice with escalating counts. もっと腹がたったら means 'if you're even more angry.' The parallel structure makes it memorable.