"crazy," 1957, British slang, perhaps from earlier naval slang meaning "slightly drunk" (1948), from notion of a thump ("bonk") on the head.

"pregnant," 1942, British slang, from pregnant (adj.1) + ending as in bonkers, crackers, starkers. This seems to be an expanded version of -er (3), the suffix used to make jocular or familiar formations from common or proper names (as in rugger for rugby, and soccer).