Meaning: oh well, never mind, too bad, tough
Literal translation: so much worse
Notes: The French expression tant pis can be either fatalistic (expressing a disappointed resignation) or accusatory (indicating that whatever happened is one’s own fault). The meaning of tant pis in the second usage is a bit stronger than « too bad »; in most situations, the best translation is something along the lines of « too damn bad » or « tough. » (In rare cases, you could even go so far as « tough sh*t, » but that expression is usually far stronger and more vulgar than tant pis.)
J’ai oublié d’apporter le cadeau mais tant pis.
I forgot to bring the gift, but oh well / never mind.
C’est tant pis pour lui.
That’s just too damn bad for him.
Synonyms (for the first usage): Dommage, C’est dommage, Quel dommage, C’est dur
Antonym: tant mieux – good, all the better