mean
Mean mean people mean mean things.
The sentence parses as 'cruel, average people intend cruel, unkind things' — using 'mean' four times in different grammatical roles.

Meanings (pronounced /miːn/)
to intend, signify, or have as a purpose
- I didn't mean to hurt your feelings.
- What does this word mean in Spanish?
unkind, cruel, or stingy
- The mean comment ruined her day.
- His landlord was mean about repairs.
the arithmetic average; the central value of a set of numbers
- The mean of 4, 6, and 8 is 6.
- Statisticians distinguish the mean from the median.
Word origin
Three etymologically separate words that all became 'mean': 1) the verb 'to intend' (Old English mǣnan, from Proto-Germanic *mainijaną); 2) the adjective 'unkind, low' (Old English ġemǣne, originally meaning 'common, shared,' from Proto-Germanic *gamainiz, related to 'common' itself); 3) the noun 'average' (from Old French moien, from Latin mediānus, 'in the middle'). Three completely different sources, one modern spelling.
Fun fact
Three completely separate words came together as 'mean' in modern English: one from Proto-Germanic *mainijaną (intend), one from Proto-Germanic *gamainiz (common, hence by social descent 'low' and 'unkind'), and one from Latin mediānus (middle, average). The triplet is among the busiest convergences in the English lexicon — three words spelling and sounding identically by pure chance.