Now why would a belligernt homophobe instruct me to "Suck [his] dick"?

Yes it is just an expression and is not to be taken literally.
[sarcasm]
After all, it is a well-known fact that homophobes do not have even the slightest inclination of engaging in any type of homosexual activity.
[/sarcasm]

Anybody who butchers the Standells that badly can suck my dick!
For the record, it’s: buh-duh-duh dah, dah-dee-dah…

“You kissed a girl? Dude, that’s so gay!!” - Simpsons