There are a multitude of ways to say "absent oneself from" depending on the context. If you are referring to missing school, you could say "skip class," "play hooky," or "sluff off." If you are talking about skipping work, you might use phrases like "call in sick," "take a mental health day," or "request time off." If you are discussing someone who regularly misses events, you could say they "no-show," "flake out," or "ghost." Depending on the formality of the situation, there are countless ways to express the act of not showing up or being present.