"An obstruction conviction cannot stand when it
is based on speech protected by an individual’s
first amendment right to criticize on-duty police officers"
Source: Amicus Brief to Supreme Court of the State of Washington in State of Washington v. E.J.J.
I agree with @DaleM's answer. And I want to add to it by picking up on a nuance of the question I don't think DaleM's answer addresses specifically.
This question might be about obstruction, not slander.
Although the OP specifically mentions slander in their question, I think the context suggests the question actually concerns something different. Like perhaps, obstruction.
- The question title specifically says, "curse [at]... an officer..."
and the OP characterizes their behavior as follows:
- "I belittle them..."
- "...and make them really think about what they're doing"
- "...what if I really embarrass an officer with something I say..."
My read of the question suggests (to me) the OP is describing "name-calling" or "insulting" the police by saying things like:
"You're an X." (where X is an insulting term or label)
A case involving facts similar to what the OP describes has recently been tried, appealed and resolved by a state supreme court.
State supreme court ruled in favor of First Amendment protection.
The Washington state supreme court ruled as recently as June 25, 2015 on a case that dealt with this issue. [The Seattle Times reports here] that the [Washington State Supreme Court has ruled in the case of State of Washington v. E.J.J.]:
"First Amendment protects profanity against police"
A teenage boy convicted of obstruction after yelling and cursing at three Seattle police officers while they were investigating a disturbance at his house had a First Amendment right to behave the way he did, the Washington Supreme Court said in an opinion Thursday.
Citizens who curse at police and call them abusive names while they’re investigating a crime are protected from arrest by the First Amendment’s guarantee of free speech, the state Supreme Court ruled Thursday in a case out of Seattle.