liarrhea

1. Diagnosis for a pathological or compulsive liar who can't keep up with their own bullshit.
2. When you're caught telling a lie and you have to keep making up your story as you go.
3. When you tell yourself you CAN handle that dish even though you know damn well you can't.

Def. 1:
A: Man, yesterday's Taco Bell with Bobby fucked me up.
B: You told me you went to Chipotle with Fred.
A: No, that was Monday.
C: No, Monday you went to Chili's with Hannah. She sent me a snap.

A: No, I -
B: Besides, Lana put you guys' lunch from IHOP on IG today.

C: Someone's got liarrhea.

Def. 2:
Teen: (was at a party the previous night, claimed to be at school sport game)
Parent: How was the game?
T: Pretty good. We won.
P: I read on facebook that you lost.
T: We won in spirit. The fact that the coach was there with his mom in the hospital is amazing.
P: I just saw her in one of his posts, too. Healthy as a horse.
T: Must've been his dad, then.
P: Cut the liarrhea, and tell me where you were before I turn the wifi off.

Def. 3:
A: Here's the Lysol.
B: Why?
A: You're eating Taco Bell. We both know you'll be having liarrhea later.

backseat dm

The "backseat dm" or "backseat dungeon master" brings a thoroughly marked and noted rulebook, and is quick to jump in whenever a rule is broken or ignored.
The nerd/D&D version of backseat driving

Player 1: That's not really how it's done, but I'll allow it.
Player 2: Wait a minute! That's against rule 534 on page *flips open rulebook*
P1: I'M the DM here. Don't backseat dm me.