。
When you know it yourself, too.
Literal
Self [even-でも] understand-[continuous-contracted-てる] [despite-くせに].
A reproachful retort. ~くせに ('despite X, even though X') is a conjunctive particle with a distinctly accusatory tone — it suggests the speaker disapproves of the contrast between what the listener knows/is and how they're acting. Stronger nuance than のに or けど. Leaving the consequence unsaid (trailing off on くせに) makes the accusation hang. わかってる is the contracted form of わかっている ('knowing').