Anyone who watches any television programmes made about Scots (though usually not by Scots) and featuring the English, will know the term Sassenach, which if you believe these shows or films, the Scots use freely to describe the English.
The reality is you’re very unlikely to hear the term these days and more often than not if you do, it’ll be used in jest.
The term originated in the Highlands and was originally used as a derogatory term in Gaelic-speaking circles to describe the English or even in some cases the Scots-speaking lowlanders.
‘The Highlanders have no other term for the people of the low country, but Sassenaugh, or Saxons.’ - Tobias Smollett, The Expedition of Humphry Clinker (1771)
Its usage has appeared now and then in modern times and is generally used to describe all English people, though more often than not it’ll be uttered by the English themselves when being self depreciative amongst Scots company.
‘That’s right pick on the token Sassenach,’ is likely to be heard uttered by English accents in Scottish pubs, as rounds are ordered and friendly banter exchanged.
The word itself comes from the Gaelic Sassunach, from the medieval Latin Saxons. The Irish also used the word Sasanach for the English, while the Welsh used the related word Seisnig. Even the mighty Cornish have their own version in Sawsnek, likely from the same derivation.
Nowadays, the use of the term is far more tame and has even been used in Journalist circles on both sides to differentiate between something Scottish and something English.
Interestingly enough, the most recent use of the word is in a new TV programme set in Scotland. Outlander, the Ronald D. Moore TV adaptation of Diana Gabaldon’s popular novel, has its first episode titled ‘Sassenach’.
Though perhaps unsurprisingly, the Author and TV Producer are both American and not Scots.