Good morning, my friend
- palerma; otário; idiota; bobo; tolo; maluco; parvo; pateta; palhaço
If we are looking for euphemistics words, it is better to avoid using this word.
Anyway, in informal contexts, specially in long-term friendships, it is quite common to use sentences like Don't be fooled / misled.
Misled sounds less offensive.
We have other examples:
Don't get your hopes up!
Don't be deceived! / Don`t deceive yourself!
Don't be cheated!
I hope we have helped.
(1) Collins Dictionary.
(2) Pearson Education. Longman Dictionary. 2004.
(3) BALDRIGE, Letitia. New Manners for New Times: A Complete Guide to Etiquette. New York: Scribner. 2003.
(4) TRASK, Robert. Key Concepts in Language and Linguistics. Psychology Press. 1999.
(5) English Oxford Living Dictionaries.