So you remind the modalist about all the Scriptures which indicate a distinction between the Father and Jesus, and they're also like Uh oh.
I don't remember if I've seen others do this, but I always point out to modalists that they, like their fellow heretics, the Arians, are unitarians.
Also, the moment they say something like
"Jesus is the Father", I point out that what they are doing is simply using two, different names -- "Jesus" and "the Father" -- to refer to just one person, instead of to refer to two persons. It may be they are 1) referring to Jesus both as "Jesus" and as "the Father" (which is asinine); it may be they are 2) referring to the Father both as "Jesus" and as "the Father" (which is asinine); and yet, again, it may be they are 3) referring to some other person (or place, or thing) that is neither Jesus or the Father, both as "Jesus" and as "the Father" (which is asinine). Actually, it also could instead be they are 4) using one or both of those phrases -- "Jesus" and "the Father" -- in a cognitively meaningless way, referentless-ly (which would also be asinine).
No one in his/her right mind would say
"The Son is the Father" while both 1) actually referring to the Son (a Person Who is not the Father) by the phrase "the Son", and 2) actually referring to the Father (a Person Who is not the Son) by the phrase "the Father", since, in so doing, he/she would be saying
"[A Person Who is not the Father] is the Father"/"The Son is [a Person Who is not the Son]".
(I use those brackets to indicate the referent underlying the phrase used to refer to the referent.)