"Election Day" joke

Two friends are discussing politics on Election Day, each
trying to no avail to convince the other to switch sides.
Finally, one says to the other: ''Look, it's clear that
we are unalterably opposed on every political issue. Our
votes will surely cancel out. Why not save ourselves some
time and both agree to not vote today?''
The other agrees enthusiastically and they part.
Shortly after that, a friend of the first one who had heard
the conversation says, ''That was a sporting offer you made.''
''Not really,'' says the second. This is the third time I've
done this today.