[long time RHPS fan]
“Let your mother do the rest!”
Or, alternately: “Incest! A game the whole family can play! By Milton Bradley!”
[/LTRHPSF]
Suck what?
“I’m not gay.”
Of course, if you ARE…
Eh, it’s what I’d say to something like that. I’m not a boy type, though, so I have nothing invested in this game. 
OP, do what I suggested and report back. 
Y’know, he never says. Whatever “it” is, I suppose.
“It?” Is that what you call your penis? I call mine “The Dominator.”
Is that better?
Brevity is the more effective soul of wit: “Show me how.”
Naw, I filled up on maturity on the way over.
This is a CLASSY place, dickweed!
Just so you know, I’m a spitter.
How about a perennial favourite, “So’s your face.” ?
I can’t find video of it, but comedian Miller Crosby had a bit about guys always telling her to suck their dick as their go-to insult. “Suck your dick? Is that really the worst thing you can think of? The most unpleasant experience you can wish upon someone? …Is there something wrong with your yours? Is it mangled or something?”
You have to own it… but I can imagine your brother saying, “suckit!” in a stilted, high pitch, tone. You can go down an octave and say, 'Suck Dis!" in your best Barry White stilted bass… you have to own it, though, you got to be goofy.
Nah, thanks but I already flossed today.
Or,
I’ll suck it long, I’ll suck it hard,
I’ll suck it like a time-punch card.
N.B. Not recommended for use by beginners - due to possibility of earning “punch-card” nickname.
“do I hafta take my teeth out again?”
Much better.
you can follow it with
‘a penis called it, isn’t that in the self help section?’
I find “eat a bag of dicks” works well for all occasions.
I thought we stopped sucking each others dicks when we turned 12.
As out said, yes, much better.
i agree to the fullest. use this statement.
“Why? Is the dog/cat/gerbil out of sorts today?”
“Hard to do with your hand always in the way.”
“Just because you like to do that doesn’t mean that I do.”