My 3 year old son is exactly the same, but we have no little one around just yet (that new one will arrive in Jan). He has been doing the same for sometime now so I was thinking it was an attention thing. Ive also noticed that if hes had a recent snack then he will play up more around tea time ... like hes not that hungry and getting bored eating when he doesnt really want to. I only say this cos when hes gone a while with nothing to eat, he will sit and eat up. Ive even tried getting him to help me make his tea .... mixing in the sauce to his pasta, buttering his own toast for brekkie/pouring milk on his cereal. Its just hard and frustrating so I know where you are coming from.
I just wish I could get him to eat a more varied diet as its either pasta, homemade chicken nuggets, soup, cheese on toast!!! Wheres the veg!!
Good luck