The campaign Tickling is Torture by international animal rescue campaigns against people keeping slow lorises as pets (for very good reasons). One claim they make however is that tickling is torture for slow lorises, something that they do not seem to explain or back up anywhere as far as I was able to find, yet it is even the name of the campaign. The best I was able to find is that them raising their arms like in those tickling youtube videos is a sign that they are preparing to bite, however in that case I would at least expect them to bite/try to attack at some point, which in turn would teach any naive pet owner that they probably shouldn't do it again, instead of doing it again and even filming it.
Just to be very clear here: I am not skeptical of the claim that they make for bad pets, nor of the claim that they probably do not enjoy the tickling (and definitely won't enjoy it in a bright lit room), but the difference between 'not enjoying' and 'torture' is huge.