YTA, official diagnostic methods exist for a reason. First of all, to make maximise the chance of getting the right diagnosis. Autism has significant overlap with other things, the overlap with AD(H)D is huge. You also want a term like autism to have meaning, and if everyone can just diagnose themselves, things start to loose meaning. For example, if everyone could just call themselves a lawyer, we'd have some very shitty lawyers. Same with autism, if everyone who is a bit quirky starts calling themselves autistic, then the general population will become less understanding of why I might need some accommodation, because the other 20 "autistic" people in the office can deal just fine.