I tell him his forehead feels warm whether it does or not - the reverse of faking sick, I guess 😉 Then tell him I want to take his temperature and to lie down while I go and get a thermometer. I make what he thinks is a joke about the most accurate way to take his temp, and tell I'll be wanting him to flip over on his tummy once I'm back. Most of these poor "sick" subjects of mine dismiss it as just that - a joke. Then there are those times I get lucky, and with a little protesting from him; and some assurance from me that it won't hurt and I'll be real gentle and it will be real quick and yes I really do need the most accurate read so I know how bad his fever is, he reluctantly agrees.
Then I go and get the glass thermometer, lubricant - sometimes Vaseline and sometimes KY (I love Vaseline so much more, but it's hard to remove and he'll be more likely to let me take his temp this way again if the clean-up is quick and easy) - and some tissues.
I sit on the edge of the bed, give him a little pat on the behind, and ask him to turn on his left side. This takes coaxing, he doesn't usually just do this. Then I lower his pants below his hips in slow, gentle motions so he trusts me to do what's most important. I'm multi-tasking at this point - responding to some of his protesting, perhaps covering what parts I can with a blanket if he's shivering, and lubricating the tip of the thermometer.
He knows what's coming next because I have one hand on his cheek and the other angling the thermometer toward his rectum. At this point, I'm usually telling him not to tense up - to relax. I may have him take a breath, and tell him exactly when it's going in, if that's what will make him more at ease. Slowly I slip the bulb inside and past his anus. If I do get any resistance, this is where, so I need to tell him something like "Ok, it's almost in" or "Good. You're doing great." Sometimes if it's too tight, I may pull back with a slight twisting motion and angle it back inward a couple of times. This seems to make him more relaxed.
I'll keep one hand on his bottom, with the thermometer between my fingers. After 3-4 minutes, I'll remove the thermometer once - slight twisting motion again - to see what reading I get. I'll re-insert it for another 3-4 minutes just to make sure I get an accurate one.
After 3-4 minutes into the second insertion, I slowly slip the thermometer from his rectum one final time. After I slide a tissue over it, I'll hold it up to the light to see what his temp is. That reading will tell me how long I need to keep him in bed and how frequently I need to check his temp.
That's my procedure!