I might use easygoing , which is synonymous with undemanding .
M-W lists it as any antonym of fussy , which can be applied to tastes in food or clothes.
One definition that fits this context is: easygoing ( adj ) relaxed and informal in attitude or standards
An example sentence might be:
Diane is really picky about what she eats, but her sister Jill is much more easygoing .
An idiom that might work is go with the flow , which Macmillan defines as: go with the flow ( phrase )
do what seems like the easiest thing in a particular situation
This may not a precise fit, but it could work depending on what you were trying to convey: Every time we go to the mall, Diane is really picky about clothes, but Jill just goes with the flow.
She'll pretty much agree to anything we suggest .
The phrase go with the flow
suggests a calm and accepting attitude.
ell.stackexchange.com/users/113/J.R.
We can use flexible , which is often used casually.
Formally, this is defined as: (of a person) ready and able to change so as to adapt to different circumstances.
In context: - "I'm hungry, let's eat!
Any preferences?" - "
Oh anything's fine, I'm flexible ."
ell.stackexchange.com/users/76100/Hanman004
I would suggest: undemanding (if speaking about food or requirements) casual (about clothing or attitude in general)
In colloquial speech (bear in mind I am a native British English speaker.
My colloquialisms may not be quite the same in American English)
you may hear: "I'm easy" in response to a question about tastes, likes, dislikes.
This conveys a casual attitude, that you have no specific likes or dislikes.
Or: "I'm not fussy" (informal) "I'm not particular" (slightly more formal)
ell.stackexchange.com/users/66325/Astralbee
If asked for a general preference, e.g. What type of X do you like ?
the most natural responses to my ears are: I'm not fussy .
I'm not picky .
I'm easy .
(adjective, sense 6)
Although easy can have a sexual connotation, most of the time it won't.
You'll get a knowing glance because of the double entendre , but people won't accidentally misunderstand.
If directly asked for a choice, e.g. What type of X
do you want ?
other possible responses are: I don't mind .
(verb, sense 3)
I'm not bothered .
I'm not fussed .
ell.stackexchange.com/users/9936/CJ Dennis
I would suggest unfussy .
It was my immediate reaction when I saw the question title.
ell.stackexchange.com/users/45825/Martin Bonner supports Monica
Easy , easygoing , and game are all good choices and already mentioned.
Since no one posted it yet, though, I'll also throw out laid back or laid-back .
The OED has it in the figurative sense of 'relaxed' since at least 1974 :
It's all cheerfully grotty and relaxed in the usual laid-back Montreal style.
Wiktionary is unsourced but claims it goes back to the '50s .
Really, any synonym for 'relaxed' is going to work here with a little context.
Some fairly popular recent slang would be chill or down for whatever .
The later can have sexual connotations as a general description, but works just fine in response to a focused question.
Whaddya wanna eat?
Man, I'm down for whatever .
ell.stackexchange.com/users/52137/lly
A less popular but still sometimes used word is catholic (lower case "c"): 2 :
comprehensive, universal; especially : broad in sympathies, tastes, or interests - a catholic taste in music Merriam Webster
ell.stackexchange.com/users/21766/Todd Wilcox
Related to Martin Bonner's and Astralbee's answers, the best single-word antonym I can think of is unparticular : adjective :
Not particular; especially not exacting, fastidious, or fussy.
ell.stackexchange.com/users/14166/hBy2Py
Relaxed is another good word: "Don't worry, she's pretty relaxed about food."
Merriam-Webster defines it as "easy of manner" which seems to fit your request.
"Relaxed" also comes up in a search for a translation of "fünfe gerade sein lassen" (literally "let five be even", i.e. don't insist on formalities, don't be fussy, be flexible — the German answer to your question).
ell.stackexchange.com/users/15471/Peter - Reinstate Monica
A word that's very similar in meaning to the adjective picky would be finicky .
The opposite of finicky then would be unfinicky which is defined simply as: not finicky You could also consider the word unfastidious which, as with unfinicky , is simply the opposite of fastidious : not fastidious: not extremely or excessively careful, selective, difficult to please, etc.
In all honesty though, you would probably be better off sticking to not finicky and not fastidious rather than the contrived-sounding unfinicky and unfastidious :
He's not finicky about the food he eats.
So, when it comes to food, he's a person that's not very hard to please.
She's not very fastidious about the clothes she wears.
In fact, she buys most of her clothes in second-hand stores.
ell.stackexchange.com/users/6450/Michael Rybkin
It may not be a special word, but in my experience, the most common antonym for picky is not picky .
"Where would you like to eat dinner" "
Oh anywhere is fine, I'm not picky.
"
"It's easy taking my daughter clothes shopping, she's not picky about brands.
"
"Did you see the guy Sheila was out with last week?
Looks like someone is not very picky..."
ell.stackexchange.com/users/11195/barbecue
What adjective would be used to describe an attitude where one is not too demanding about something (like the food they eat, the clothes they wear, etc.).   I'm looking for a word that sounds fairly informal or colloquial.
What is the opposite of 'picky'?
ell.stackexchange.com
<word-request>
ell.stackexchange.com/questions/167942
ell.stackexchange.com/users/76072/user18894
Relaxed, easy-going, flexible, and undemanding can all be used in this context. Alternatively, one might say "I'm not picky", "I'm easy" or "I'm not fussy". Relaxed' or synonyms like 'easygoing' or 'flexible' are often used. Someone's attitude could be described as undemanding or casual. When talking about our own attitude, we could say "I'm not fussy/bothered/fussed/picky", "I don't mind" or "I'm easy".
Relaxed' or synonyms like 'easygoing' or 'flexible' are often used. Someone's attitude could be described as undemanding or casual. When talking about our own attitude, we could say "I'm not fussy/bothered/fussed/picky", "I don't mind" or "I'm easy".