I liked Tottenham until they got Mourinho, but I never supported them.
Supported Man Utd when they had Peter Schmeichel, but for the past 20 years I have supported AC Milan.
I saw Arsenal - Milan at Etihad and met lots of Arsenal fans before, during and after the match, a draw. In the Tube and on pubs. It was just friendly banter, like "You got dirt on your red shirt", and they were singing supported songs. (I don´t know any italian songs)
Same around 2000 when I was in an Arsenal Pub and insisted Keane was as good as Vieira. No hard feelings, just a discussion between fans.