I Got 5 On It Operation Stackola Luniz

fools be havin' them vacuum lungs

Luniz is saying people inhale the marijuana like a vaccuum would suck in dirt.
Yukmouth is expressing his displeasure at the fact that whenever he finds it within his heart to share his marijuana with someone, they tend to over-indulge.
An analogy to explain that when smoking weed, one might inhale a lot without seeing many side effects....such as a vacuum.
Stupid people inhale the weed smoke like a vacuum. (Basically smoke more weed than would be acceptable given the circumstances.)