How about a dwarf (as in the fantasy race) ringmaster berating a tramp clown; the airhose from the clown's pump or helium tank going down the ringmaster's pants and filling him with predictable results. Or perhaps both with hoses into their trousers.
In the first case, the ringmaster could be screaming at the clown that he's not a balloon, in the second case he could be furious because there's no one left to shut the gas off and he's afraid they're both going to explode.
Welcome to the community otakumew. ^_^
I normally don't request something from other artist that much because I would normally make them myself but since you said you need to practice on inflation art I'll help you out.
Can you draw Bridget from Guilty Gear X inflated in any way you see fit. His feminine attitude, wearing, and voice is just asking for it lol. =D