1. Columbo mentions his wife. Columbo does not in fact have a wife but a harem of nubile wenches eager to debase themselves for his every trenchcoated whim.
2. Columbo turns up completely at random in a stalkery way (two drinks if it is at a sporting event).
3. When there is a close up of the bad guy looking smug (you know the look of “ah this crumpled fool he will never catch me for my fiendishly over complicated murder plot”)
4. When Columbo destroys evidence.
5. When he says “there is just one more thing”