Watched a guy at the parts counter in Boise press a caliper piston with channel locks and ruin a $95 core, so I stopped loaning my $22 tool | Brake Pad Diaries - Rigidtalk
Loaned my puller set to a buddy once and got it back with the screw threads all chewed up from him using a impact on it. Now I just tell people the tool box is closed, go buy your own.