Whirly, you and quite a few others here seem to confuse W&B with MTOW. Two average sized adults and full fuel will put you slightly out of CofG (forward) on a PA28, however it will NOT put you over MTOW.
It is also true that two average/large adults and full tanks will most likely be over MTOW on a C152 where most dual hours are being logged.
Or even worse on a DA20 on which I logged quite a few PUT hours.
I don't recall any mf my instructors defuelling or doing a 15 min run up to burn off fuel !
Like everything it's common sense, don't think that 10 kgs over, on a long tarmac runway , is a major sin.
Different story on short grass strips / adverse weather / wind / temperature conditions.