1st obtainable achievement :
As soon as you get the clown costum during the tutorial in the aligator park you just have to smash B for using the horn 1000 times while wearing the clown costum. It took me me about 4 minutes !
The clown costum is not missable because it is story related.
Very good Trick from Al Rajul
: If you miss this during normal play through, you can still accomplish it during the credits.