Insanity. I grew up in and near Birmingham in the 60s and 70s, and should by rights support Villa, who are my second fave team, for reasons indicated below.
My dad, a staunch Irish Republican, followed Shamrock Rovers and Celtic. His numerous brothers (one of whom had played for Shamrock briefly) all lived in Southend on Sea, and were Spurs, Spammers, or Goons, but mostly Spurs. That, and the fact that I liked the strip, and the presence in the team of Greaves, Mullery, and so on, probably made my mind up for me, aged about nine or so. My big bro chose Man U, and my little bro (now dead, alas) chose Villa. My youngest bro is not a footy guy. My late brother's eldest son is a professional football journalist in Toronto, and loves Villa.
At some point (I think around the time of Fever Pitch) my big bro became a vague sort of Goon, and his son is a staunch Goon. We banter. My ex wife works in telly and is a Groucho Club Chav - appalling!