Cheated
Dog crap
candy from baby (child, not baby though...and they were asleep and I thought they had forgot about it

)
Lied on taxes..but only if this counts...didnt inform DWP that I had returned to work when I was like 17 until a fortnight after I had started, so as to claim an extra fortnights money to tide me over til payday

(I figure they are the same thing in a way)
Borrowed something and not returned it
Cut in line
Cheated at board game
Filled water with sprite (or coke, as was the case

)
Kept library book
Made up statistics...I do this a lot in real arguments if I think I'm losing. Only among friends though
Oh dear thats quite a lot