According to Robert Payne (Hitler's biographer), the vegetarian claim was made up by Goebbels to give the impression of an ascetic in the manner of Ghandi; Goebbels claimed that Hitler did not smoke, drink, eat meat or have anything to do with women. In fact, it is known he did all of these -- except smoke.
"You're a vegetarian, between meals"!
In much the same way as someone would give up smoking in-between each cigarette.
"Giving up smoking is easy....................I've done it hundreds of times".
Erroneously attributed to Mark Twain.