Inventing new (wrong) plural forms is something I find very entertaining. My favourite is obviously the "-en" version.

• Nagellachse (Nagellack)
• Kacktusse (Kaktus)
• Kürben (Kürbis)
• Penen (Penis)
• Avocaden (Avocado)
• more good words: bekuscheln, Elumpanti