wet noodle

Short definition from Wiktionary

Noun

1. 1
   A noodle that is freshly made, before it dries out and becomes rigid.
2. 2
   A means of enacting a mild or ineffective symbolic punishment.
3. 3
   A wimp.
4. 4
   Someone or something that is limp, relaxed, or weak.
5. 5
   A man with erectile dysfunction.
6. 6
   A flaccid penis.
7. 7
   A weak handshake.
8. 8
   Wet noodle.