Addressing aggression in youth requires understanding of the range of social problem situations that may lead to biased social information processing (SIP). The present study investigated situation-specificity of SIP and analyzed whether SIP deficits and biases are found in ambiguous as well as clearly accidental situations in adolescents with clinical levels of externalizing behavior or with low intellectual level, congruent with mild intellectual disability. Adolescents (N = 220, Mage = 15.21) completed a SIP test on a mobile app with six videos with ambiguous, hostile, and accidental social problems. Caretakers, teachers, and adolescents themselves reported on youth externalizing behavior problems. In accidental situations specifically, adolescents with low IQ scores more often attributed purposeful intent to perpetrators than peers with borderline or average IQ scores. In accidental situations, adolescents with clinical levels of externalizing behavior generated and selected more aggressive responses than nonclinical adolescents, regardless of their cognitive level. In line with previous literature, the ambiguous situations also brought out SIP differences between IQ groups. These results suggest that not only ambiguous situations should be considered informative for understanding SIP biases, but situations in which adolescents are clearly accidentally disadvantaged bring out SIP biases as well, that may lead to conflicts with others.