Exactly as it sounds, a "yank your doodle", in common terms, puffed up, a dandy, a wanker. A person with an inflated sense of their own importance. A person whose fantasies exceed their abilities.
A Middle English expression. Ye is pronounced 'e by all except the upper classes. Yank'ee doodle.
Yankee Doodle - Dirty Peasant One speaks to Dirty Lower class labourer Two about a well dressed young gentleman passing by, "Yank'ee doodle"