Remember that thing on the previous page about how condoms and wallets don't mix? It's not just the heat-friction combo ... there's also the out-of-sight, out-of-mind factor. That sad, lonely condom, tucked between old receipts and tattered bills, may be long past its prime by the time anyone has a need for it. Condoms have expiration dates for a reason – old latex becomes brittle, even if it's been stored somewhere with much better climate control than a back pocket.
First step: Check the date on the package. If it's in the past, pitch it. Second step: Look at the condom itself. If it's dried out, sticky or brittle, it's too old to use. Throw it away.