Mrs. Doubtfire throws a lime at Stuart’s head. Could Stuart get him in trouble for assault?
Yes, this could conceivably lead to criminal charges. A common confusion is the difference between “assault” and “battery,” in states such as California which distinguish between the two. Assault consists of a threat of force that would lead a reasonable person to believe that the defendants’ act would result in force, combined with the defendant’s ability to actually apply force to that person. Battery, on the other hand, is when you actually make contact.
If Daniel swung the lemon wildly and threatened to throw it at Stuart—assault. Once it hits him, battery. “Stuart” likely deserves it for his later work in the Thomas Crown Affair.
Okay, let’s get into specifics: at one point in the movie, Mrs. Doubtfire pulls the hood ornament off Stuart's Mercedes. Could he get in trouble for that?
Yes, this could conceivably lead to criminal charges. In California, Daniel could be charged with vandalism, which—despite the connotation with graffiti artists or troublesome kids—really means any sort of malicious destruction or damage to property.