This section from the NetBSD man page for the sleep command cannot be funnier, yet completely valid. I mean, quite useful if you have the time, right?
BUGS
This sleep command cannot handle requests for durations much longer than
about 250 billion years. Any such attempt will result in an error, and
immediate termination. It is suggested that when there is a need for
sleeps exceeding this period, the sleep command be executed in a loop,
with each individual sleep invocation limited to 200 billion years
approximately.