A Sussex
To do ‘A Sussex’ is to have sex with someone who is sus. You're not just having sex, you're questioning their whole life.
'He’s sus, I had sex with him and now I don’t trust him anymore.'
'She’s sus, I asked her to marry me and she said no, then asked me to marry her ex.'
'He’s so sus, I had sex with him and now I’m questioning my whole life.'