I'm going to tell my girlfriend that another girl was hot
Why would you say that to her?
I want to tell her but I dont' want her to be suspicious of me.
It's not advisable to tell your girl that you find another person hot. It will cause unwanted dramas in your life.
I just want to see her reaction hahaha.
Even still, there's no need to upset her on purpose and you should keep it to yourself.