> Can a gay person be a homophobe?

I'm not sure if you're asking this question in seriousness, but... yes, gay people can be homophobic. A significant proportion of the population is gay, and every one is unique.

http://gayhomophobe.com/ focuses on anti-gay campaigners who have been caught in gay sex scandals. George Rekers is possibly the most familiar - dedicating his life to anti-gay campaigning while travelling with a personal rent boy.

The simplest polite thing to say about Brian Sewell (who you quote) is that he doesn't represent the wider gay community.