Riddle

Air bubble

An oil slick?

I was thinking of steam, hydrogen/oxygen etc. but I'm not at all sure

a crocodile, or a hippo or maybe a german submarine at halfmast

Not really getting anywhere with this, might not be smart enough...
But could it be, that it is a word, that is made up of some of

A I R W A T E R

and if you scramble the letters up, it's meaning becomes 'grumpy'

?

could be ...ier as in more ...y, therefore VERY grumpy.

(Just throwing it out there)

senior citizens in a spa

Irate.

part of me is in air - IR
and part of me is in water - ATE

Mix me up and I'm grumpy. IRATE

Ha, I knew it, even if I was too stupid to find the solution!