Why is my toddler having 'accidents' on purpose!? ARGH. Should I give up?

[BayLeaves]

DS turned 2 last month and took an interest in using the potty which has been sitting dormant in his room for a couple of months now. I wasn't going to start potty training at this point, but after doing a couple of wees and a poo on the potty a few weeks ago, I thought why not try it while he's keen.

So for the last week we've been potty training with chocolate buttons and stickers as bribes. It was going fairly well, we got down to just 2 wees on the floor yesterday and the rest on the potty, and all poos on the potty consistently for the last two weeks now (before we even stopped using nappies).

Today I was at work and DH has DS for the day. All day long he weed on the floor on purpose and did hardly any on the potty. At naptime he wore a nappy as usual and he did a poo in the nappy after waking up from his nap. I was gutted as he's basically been potty trained for poos for weeks now.

We then had a bath together and he looked at me dead in the eye and said "poo poo bath". I said NO! NO POO POO IN THE BATH! and you can guess what happened next. Yup, his face goes bright red and that's when I leap out the bath. Sure enough, there goes a floater... This was no accident, I am 100% sure he did it on purpose. Grr!

He's kind of become generally naughty recently though. We went from having a lovely happy jolly baby with no tantrums, to a tantrumming, fussy eating child who pulls ugly faces and says "NO, go away!" to everything. Sigh. Is this just the terrible twos? Should I give up on the potty training after a fairly okay week?