Yeah, apparently it's a pretty bad insult, everybody always stresses its importance. To quote a grammar site (http://www.studyspanish.com/lessons/persa.htm):
"From the perspective of the English speaker, the personal "a" appears to be an extra word. From the perspective of the Spanish speaker, the personal "a" is required, and to not use it is a serious error."
It's like not saying 'do/will/etc' in questions
'Do you like coffee?' correct 'You like coffee?' incorrect
'Will you come?' correct 'You come?' incorrect
Like Elizabeth said, to Spanish speakers, the word 'do' is just an extra word. But to us English, you have to use it
Except in slang, etc.
Dejar + a = to leave
Dejar + de + infinitive verb = to stop (doing that verb)
Dejar = to let/allow
so is the 'a" after dejar there to make it "leave" instead of "allow" or is the "a" there as the "personal" a?? It's probably both but if you wanted to say "she ALLOWED her boyfriend "the personal "a" would still have to be used wouldn't it? ( because the direct object, her boyfriend, is a person) and therefore the sentence would be the same ie dejar would be "leave" Thanks.