Square

(1) Unexciting, unadventurous, mainstream or dull. Generally used in describing a person with such attributes or who plays it safe. Historically, derived from a person whose goal in life is to have three "squares" a day (see definition (3) below), a roof over his head, a respectable job, a house, 2.5 kids, etc. Became a hip/popular expression of derision of the mainstream in the beat generation.

“Simmy is a square”