uh-oh, UH-OH!! time for you to switch definitively from MBTI to socionics!!
BLASPHEMY! Ti Se is my conflictor!! It's ISTj in socionics.
The ISTPs you know are probably not socionics ISTp's. MBTI type does not translate to socionics (it may coincidentally, but that would just be coincidence). Though I have to say he partied hard but didn't really suffer for it (or so it seemed). . .I dont think he took any hard drugs, he just drinks a lot.
The ISTp (SLI) that I knew probably is an MBTI ESTP.
Anyway so, socionics ISTp is Si Te. Si is their most FAVORITE function