Ah. Well, then, HG. I suppose it would be true to say that, yes, dizzycatnip
can sue his ex-girlfriend (the lawsuit will just not go very far).
What is said in police reports is covered by a qualified privilege (defeated only by a showing of actual malice) and statements made under oath are considered absolutely privileged. Neither police report statements nor statements made under oath can be used to support a defamation suit (generally). In addition, the statute of limitations would bar any defamation suit from being filed at this point.
And, because an ACD is not a finding of not guilty or a dismissal in dizzycatnip's favor, which is required for a malicious prosecution suit to go forward (as nicely detailed by Stevef with his case cites), a malicious prosecution suit seems out of the question.
BUT, if dizzycatnip has time and money to blow, he can file suit against his ex-girlfriend and then watch while his suit get dismissed.
As a note to dizzycatnip: The fact that you were arrested and charged and granted an ACD may still need to be disclosed on some employment applications. You may also wish to do a background check on yourself to make sure the arrest and charge does not show up - many background check companies mine arrest data but do not update their records to show that arrests were in error, that charges were dropped, that convictions were overturned. If errors appear, contact the background check companies for information on how to get the information on you removed.
As another note: I must type REALLY slow, because both Zig and Blue Meanie beat me to the "yes."