When you get them riled.

When a close relative dies...I almost forgot about that...seems to be one in nearly every family...the one who rushes to the house and grabs up whatever they can take before consulting with the other close relatives. And sometimes they take everything, had a sister who took everything when a relative when into the nursing home, took all she wanted and gave the rest away to strangers. That was and is her true character....even worse than selfishness and greed, it's spite and hatefulness.

1. When they're angry
2. When they're hungry
3. When they're driving
4. When they're down to their last dollar

Either when they feel relaxed around you, or if they feel threatened..

When they think they are above the law (in power) or when they think nobody's looking.

When they're in the lion's den!

When they're drunk is a good one because it lowers their ability to put up the fake front we all walk around with everyday.

Over time. It does show in one or two incidents.

When they have the advantage :/

After a couple of drinks

I also find another great way to tell a persons nature is to see how they treat and talk to strangers like waiters etc.