Fannycake is an expression describing someone who is behaving or acting in a silly manner or is just generally a silly person but you still love them despite of that.
Person 1: She is so silly getting with the wrong guy, still a lovely girl though.
Person 2: Yeah, what a fannycake!
A complete and utter twat, dickhead, plonker for whom the words 'fanny' and 'wanker' just dont elicit the right level of bastardness of said person by themselves but when put together it totally describes the person and their pointless existence.
A referee from Glasgow at an Old Firm Derby Game when "That ref used to go to St Mungos School, haw ref ya fannywanker the ball was out!"