Nice contest!
Good luck in learning a new language :D

Here are my entries:

Picture/Idiom #1
SERIOUS: Don't become cold-hearted. Protect yourself from negative people.
FUNNY: Be better than the Titanic. All you need is a flower and a pokey stick.

Picture/Idiom #2
SERIOUS: Stay smiling and don't let anger get the better of you. Let off a little steam (steem?) in other ways.
FUNNY: Next time someone asks for a snack in your home, tell them "Yeah, ok, let me get right on that.".

Picture/Idiom #3
SERIOUS: Red caps are for negative people, while blue caps are for the happy folk. Which one are you?
FUNNY: (nothing)