Ignorance: There, Their and They're:

It may be purely laziness, but more often than not when someone else points out the misuse of 'there', 'their' or 'they're', the person misusing it is simply confused.  It's not very complicated to be honest, but it is a very frequent issue.

'There' is use for indicating a location, such as 'go over there', or 'there are five wolves'.  This helps to differentiate between that and 'here are five geese', as the wolves are further away, and not immediately slaughtering and eating said geese.  It is usually preceded by the name of the location if it is not within eyesight, used as a simplifier so one doesn't always have to say 'five wolves are over by the treeline beyond the river' every time when referencing where the wolves are.

'Their' on the other hand, refers to possession.  The five geese in the previous example are owned by five farmers.  Therefore, the geese are 'their' property.  'Their five geese are here and the five wolves are there.' would be grammatically correct.  Without the prior reference to the farmers, however or a reference immediately after the sentence, we don't know who the geese belong to.  They are 'their' geese, but whose are they?

'They're' is used as an abbreviation for 'they are'.  If the wolves were crossing the river, 'They're trying to brave the river currents between their side and the geese.  The wolves mouths open, their sharp teeth eager for the taste of goose.'  This last example uses all three frequently misused words correctly, and should clarify things for those who didn't previously understand.  Those that are merely lazy, however, just need a foam bat to the side of the head perhaps.