| Abbreviation | Definition |
|---|---|
| SI | Slow and Ignorant |
| SIA | Superman's Insurance Agency |
| SIC | Sarcasm Is Contagious |
| SIC | Society of Indigent Cattle |
| SICK | Sad Isolated Cold Kid |
| SICK | Serious Idiots Clown Killing |
| SIFB | Sleep Is For Billionaires |
| SIG | Sure Isn't Glock |
| SIH | Suffering Is Hip |
| SIJ | Shake It, Jacob |
| SILLY | Slightly Intelligent Largely Laconic Yeti |
| SILVIA | Someone I Like Very Intensely Always |
| SIMA | She Is My Angel |
| SIN | Success Ignoring Nature |
| SINA | Society for Indecency to Naked Animals |
| SING | Something Inbuilt for Nature's Good |
| SINGLE | Stay Intoxicated Nightly, Get Loved Everyday |
| SINGLE | Stress Is Now Gone Life's Easier |
| SIR | Slave I Remain |
| SIR | Superior Information Robot |