My daughter (3) has the habit of insisting that I converse with her in cartoon or muppet voices on many occassions. If she calls out to Cookie Monster/Goofy/etc, she gets frustrated if I answer in regular "Daddy" voice. Saying goodnight, she'll call out to my entire repertoire as I make my way to the door.
Lately, we do a little "Baby Robot/Daddy Robot" routine with respective voices and dancing (The "Robot" of course), that cracks us up like crazy. Wish my wife was as entertained.
Her phrases of choice have been:
"Gimme some space."
"Gimme a break."
"Dirty darn!" (my wife's influence)
"Lay me some skin!" or "Gimme 5!"
"Rock on!"
"Um, excuse me, can I talk to you a minute?" (usually when she's been caught in the act and she wants to hide something behind her back= misdirection)
Unfortunately, she also picks up the "bad behavior" phrases from her kiddie shows (Franklin, Little Bear, etc) that actually try to teach against those bad behaviors. She learned how to verbalize her pouts with "I don't care!" and "No fair!" from these type of shows.
When she wanted to get up from the table (which is usually after a bite or 2), she used to say "I'm full!" After a bit, I started to respond with "Your full of baloney...". Since then, she now says "I'm full of baloney!" when she's had enough of what she's eating. Hilarious.
EDIT: Added more as they occurred to me.