Having intrusive thoughts is really awkward, especially if you have OCD
You just be chilling and then your brain is like, "no haha but what if we killed them haha, like imagine how evil that would make you haha, and omg their family members would be so devastated, could you imagine their family members sobbing in the courtroom with you on trial, like omg that would be insane right? Maybe you are evil lol. You're thinking about it right now! I bet you're inherently some kind sick fuck-"
you swore before hand that were just thinking about what you should both eat, you looked friend a bit too hard in the eyes, and now your mental illness is trying to convince you that you were secretly a super murderer in disguise the whole time
even if the follow up thoughts are...
"No, what- WTF why would I think that-"