The only specific 'threat' to Portugal that I haven't seen elsewhere is the drug dealers, which will approach you openly right in the middle of even the most touristy squares selling you weed etc. Just shrug them off and they will stop bothering you.
Now I don't think you are the type to be actually interested in drugs, but if you are: don't buy it. The openly dealing dealers all sell phony fake stuff. If the police catch them, they will only get a small fine and will start dealing their fake stuff again (they can't be caught for actual drug dealin because what they are dealing is fake).