I faked a fever first time when I was 12,because there was a test in school to which I felt not prepared in a good way. Luckily my mom was in a hurry so she inserted the thermometer in my bum and left the room. Before she came back I had taken the thermometer off my bum,, holding it at the lamp on my desk next to my bed and reinserted it with a temperature of 39,5 I guess. I trained it before so I was a lucky boy that my plan worked.
Then my mom saw the temperature which showed the thermometer, and told me to stay in my bed and in that position (I laid on my right side). When she came back to me, it was more running than going because she had to leave for work, she quickly pushed a suppository in my bum. At that point of time I was afraid that the suppository would cool me down from normal temperature to hypothermia, because I faked my temperature (don't be afraid, at age of 12 I didn't know it better, I even thought that fever has something to do with my bum because it was measured and treated there).
My mom also advised me to go to the pediatrician so I can get an official permission for school and he might find out what is going on with me. While my mom drove to work, she almost made a phone call to the pediatrician.
When I went to him, I was measured again, and I was really lucky to hear that my temperature is normal and not too low (otherwise they found out that I had faked a fever, so I believed as a 12yo). That I had no fever there was easy to me to explain, because I received a suppository earlier. I was ashamed a bit when the doctor said (he took my temperature in my bum as well) that he could see some rests of the melted suppository at my hole
But finally my plan worked, and I realized that no one will find out after getting a suppository that I faked my body temperature.
I repeated it when I was 14, nearly same situation, my mom was in a hurry, and I had the chance to heat up the thermometer at the lamp on my desk. I saw that trick in an old film (E. T.), unless the boy had to hold the thermometer in his mouth I guess what I didn't understand why and my parents told me that this is not accurate and acceptable. However, I faked with success. But I had to ask for a suppository, because my mom first didn't want to give me one. I guess she just forgot it. The rest was the same. And I could repeat it a week later, because I wanted to meet a friend of mine who did the same thing, but was caught at the second time.