I think sometimes we can expect too much from children and what we may view as 'naughtiness' is quite simply childish behaviour- and if you cant behave like a child when you are a child then ....
Do people comment upon his behaviour?
Does he know that you find his behaviour with other people naughty??
It could be that he behaves like this to amuse other people who perhaps view it lighter than you.
Depending on his age there are lots of strategies you can use and only trial and error will help you find the one that works for him.
*continual reminders of behaviours you expect.
*rewards and praise
*exact instructions of your expectations
- reward charts and behavior records
*talking it through and looking at what precedes this behaviour
Generally just riding the storm til he/she becomes a teen and you wish behaviour was all you had to worry about - now theres mobile phone bills to consider,coursework,curfews,exams,fashion clothes,secrets,moods,filthy bedrooms,astronomical food bills,the general teenage smell ...etc etc ...u get my drift?
You are not a bad mum in any way (or if you are so am I and all other mumsnetters).