ITT we talk to ourselves

Ever had to, as a gm, have a NPC talk to another NPC? How do you do it? do you have a player take up one PC? talk to yourself? Something else?

I make notes about each NPC's personality and motives and make sure to use different voices for each. That helps me move back and foth

Since I run a text game on roll 20 for one dude, I do a bunch of npcs, it's pretty fun

No experience myself, but that really sounds like something you should generally avoid having to do. Unless you've just arranged things wrong (DMPCs being the prime offender) there really shouldn't be many conversations the players are party to but not the ones being talked to, and most of those can be summarized instead of awkwardly acted out.

I only act out characters the party interacts with. If two NPCs interact separately then the conversation is summarized.

I simply insert descriptions of the events happening in-between bits of dialogue. Avoids the end result of looking like a one-man Broadway play and also helps the players keep track of who is saying and doing what.

You talk to yourself. I have NPCs interact all the time, but I try to keep it short. The switch-off between NPCs is a bit awkward, so having an extended dialogue between them is less than ideal. But having one NPC say something and another respond to it only contains 1 switch-off, and isn't that bad.

how about eavesdropping and playing on player's asumptions?
summarizing could kinda kill the mood

>Ever had to, as a gm, have a NPC talk to another NPC?
No, because that sort of masturbation is bad gming.

It is bad GMing when the players in question require constant direct stimulation and engaging with the setting is not in their nature.