The Blob (1958)

In this low-budget, campy teen, alien invasion horror B-flick from director Irvin Shortess Yeaworth, Jr., featuring the first major starring role of a young Steve McQueen:

• the scene of Steve (Steve McQueen) and teenaged girlfriend Judy (Aneta Corseaut) who tried to convince Pennsylvania townspeople and police officials that an amorphous, gelatinous, protoplasmic, purplish-red alien Blob was attacking: ("Well, it's kind of like - kind of like a mass. It keeps getting bigger and bigger")
• the memorable scenes of the Blob menacing a medical facility, a car mechanic, a supermarket, and the Downingtown Diner
• the Blob's assault on a movie projectionist's booth during a midnight movie theatre show at the Colonial featuring Daughter of Horror (1955) (aka Dementia) - causing teenaged movie-goers to scream and race out into the street