We did say things like "don't be a Benny" here in the Scottish Borders in my youth and yes AFAIK it was very much to do with Benny the character in Crossroads who had a bit learning difficulties. So aye I think it was a bit derogatory to folks with learning difficulties. Personally I wouldn't use that term now and wouldn't look to use "throw a Paddy" either as obviously it could potentially offend. Though it seems pretty clear that folks are probably using it quite innocently maybe not even connecting it to anything to do with the Irish.

On a newsnet group which was about Scotland but was mostly Americans and Canadians etc they took to replacing the E with an * in anything to do with England. It was just a joke as is the Voldermort name which can't be mentioned type thing. My English wife saw it continually written as *nglish though and she thought it offensive. It hadn't struck me that folks might take it seriously but she did. So I stopped using it. My adage is if you know something might be offensive to someone then why use it??? That is just me though....