According to the Hollywood Reporter, as she clasped the gong in her hand, Emma Thompson decided that this would be the perfect opportunity to voice her exact thoughts on the mistakes that she has made in her career.
However there is also an outside chance that she could have been talking about her appearance in another of her films. Maybe she was chastising her brief turn in Men Black 3, or her un-credited portrayal as Dr Alice Krippin in the opening scene of I Am Legend or even her performance as Arnold Schwarzeneggers love-interest in 1994s Junior. Theres even a suggestion that her portrayals as Nanny McPhee in the 2005 fantasy film and its sequel, Nanny McPhee Returns were the intended recipients of her "attack." But the fact that she also wrote the latter two films means that she would only have herself to blame if she didnt like the character she portrayed.