MAMMALIAN

Got on my back paws - got on my hands and knees. Like how animals can stand up as a trick.

ex: yeah, i really wanted that necklace, i had to get on my back legs so she would get it for me.

Showing fang - standing up for yourself/being assertive. 

ex:  he’s really tough, and he’ll show fang at just about anything.

White eye - going crazy/really scared. Like how animals show the whites of their eyes when very agitated.

ex: haha, i saw how scared you were during that movie, you went all white eye at the end!

Howling at the sun[wolf/werewolf] doing something completely ridiculously/incorrect

Ex: dude did you see how that movie ended? Mc was really howling at the sun

Could hear someone purring[cat, any other purring animal]  noticeably becoming relaxed around someone/something

Ex: I saw you with your new plush yesterday, I could really hear you purring

Treetop chaser - (herbivorous) someone who chases unattainable things.

ex: they’re way out of your league, don’t be a treetop chaser

Bellycrawler - someone overly submissive.

ex - you have to stand up for yourself, don’t be a bellycrawler and let them take advantage of you.

Downy - young, referring to the soft fur of young animals. 

ex - she shouldn’t be out til midnight, she’s still downy!

Sit on your wag - means the same thing as swallow your smile.

ex - i got accepted into college, but my sister wasn’t, so i had to sit on my wag.

Go for the ruff - do something harmless/gently.

ex - the shirt was really ugly, but i went for the ruff so i didn’t hurt his feelings.

Flea - an insult meaning antikin, or a bigot in general.

ex - oh, you have him in your class? Be careful, he’s a total flea.

AQUATIC

Riptide Rider - (aquatic) someone who lives dangerously.

ex: stay away from her, she’s a riptide rider, you’re bound to get hurt.

Current crazy - someone who just follows other people, same as flock brain

ex: my brother joined the football team, and now he’s all current crazy.

Bottomfeeder - an insult for a low-class being.

ex - the boys at my school are such bottomfeeders, they make all the girls uncomfortable.

Floater - an insult for a superior or snobby person.

ex - ugh, they’re such a floater. They brag about their promotions ALL THE TIME.

Seen the whale fall - someone who is very experienced, now become a word for old among younger aquatics.

ex - my gramps has really seen the whale fall, he’s almost 95!

Play remora - like devil’s advocate, because remoras stick close to sharks.

ex - i don’t wanna play remora about this, but i think he was lying.

AVIAN

Flock brain - (avian) someone who can’t think for themselves. 

ex: ugh, she’s only hanging out with them now, she’s being a total flock brain.

A hummer with an eagle - (avian) someone who is clearly out of their depth.

ex: are you sure you can handle advanced classes? No offense, but you’ll be a hummer with the eagles.

Mantling over [smth] - [avian] being possessive, traditionally over food items 

Ex : Sarah is really mantling over that burger menu, I tried to take a fry and she almost bit my head off...

All preened up - [avian] well dressed, well groomed, the state of satisfaction and confidence that comes with A Good Look

Ex : Wow, Eric was all preened up this evening. I don't think I've ever saw him take this many selfies. 

And just for fun...

Going for the rattler - [roadrunner] choosing the hard or dangerous option, with expectation of either great fun or a great reward

Ex : "Huh, this park offers either a canyoning session over rapids or a day in the sun near the lake" "well I'm definitely going for the rattler" 

flare(s) my wings - (avian) makes me tense/nervous/angry 

"i don't like him, he always makes me flare my wings" 

makes my wings flutter - (avian) makes me happy/excited

"pasta always makes my wings flutter"

im pretty sure "ruffles my feathers" is a preexisting one

messy wings (with no time to preen) - (avian) having a bad day/stressed (and haven't had time to cool down)

"yeah today my wings are so messy and i haven't had time to preen"

Having a blood feather - [avian] being particularly irritable 

ex : Don't bother with this guy, he's been having a severe case of blood feathers. He'll jump at you for anything.

Riding the updraft - [flying creature] taking advantage of good opportunities, being lucky in life, having an easy time.

ex : I've been really riding the updraft recently ! Got both a promotion and a new car! 

Beak agape - [avian] furious, about to throw down.

ex : Jesus, this dude really left me beak agape. The audacity to say that !

Feeling clipped - [avian] feeling restless and anxious, like there's no way out

ex : Honestly these last few weeks have left me feeling clipped, between the news, and being dropped from my job. 

REPTILIAN

Makes my scales itch - (draconic) said about something unsettling or that just feels wrong deep down, a gut feeling that something's wrong

ex: We should get out of here. This place is making my scales itch.

Blow fire - (draconic) be extremely angry about something

ex: Did you hear what went down the other day? John was really blowing fire at Derek over that one.

Rattle someone's scales - (draconic) to unsettle or upset someone

ex: Can't stand that guy, he really rattles my scales. 

Cloudy day - (reptilian) usually used as a question, if someone is acting tired or unusual. Like how reptiles need the sun to stay warm, if it’s cloudy, they can’t warm up.

ex: woah, cloudy day? You look like you haven’t slept in months.