Up in Smoke (1978)

 

Two stoners unknowingly smuggle a van - made entirely of marijuana - from Mexico to L.A., with incompetent Sgt. Stedenko on their trail.

From memory: At the time a hilarious cult stoner movie this comedy does start off with some genuinely funny moments, but very soon deteriorates into bad slapstick and crude humor.

Halliwell (no star): "Direly unamusing; the slapstick is badly timed and the humour infantile. Stoned or sober, Cheech & Chong are the least funny comedy team since The Three Stooges."

Maltin***: "This silly pothead comedy breaks down all resistance with its cheerful vignettes...Nothing great, but undeniably funny..." 

Cheech and Chong's Next Movie (1980)

The two stoners and their friends go through another series of crazy, drug-influenced misadventures.

From memory: Stoner hullabaloo  with humor appealing to the initiated only; a minor cult at the time, but obviously very dated by now.

Halliwell (no star): "Totally repulsive comedy which gives a bad name to self-indulgence."

Maltin*1/2: "After an auspicious debut in UP IN SMOKE, the pothead, put-on comic duo go seriously awry in this crude, incoherent film, which offers only sporadic laughs."