What does the underlined, "mess with" mean in the context ?

I see "mess with " have some various means.
What does the underlined, "mess with" mean in the context ?

------- The script goes in a sitcom, "Friends"

Rachel: No. Joey, she knows! We were at Ugly Naked Guy's apartment and we saw them doing it through the window. Actually, we saw them doing it up against the window.
Phoebe: You know, we saw them fornicating. Okay, so now they know you know and they don't know that Rachel knows?
Joey: Yes, but y'know what? It doesn't matter who knows what. Now, enough of us know that we can just tell them we know! Then all the lying and the secrets would finally be over!
Phoebe: Or, we could not tell them we know and
have a little fun of our own.
Rachel: Wh-what do you mean?
Phoebe: Well y'know every time that they say that like they're doing laundry we'll just give them
a bunch of laundry to do.
Rachel: Ohhh, I-I would enjoy that!
Joey: No-no-no! No-no wait Rach, you know what would be even more fun? Telling them.
Phoebe: That doesn't sound like fun.
Rachel : No.
Joey: So we'll make it fun. We'll do it like a barbershop quartet! We know, we know, we know.

Rachel: So umm, how-how are we gonna mess with them?
Joey: Ugh.