When the check came FIL excused himself to go to the bathroom and MIL looked away. Seriously.
ooohh boy, that brought back a memory.
This crosses the line from cheapskate to scammer, imo. I worked for an organization and for functional reasons our small section was located in a different part of town than the main office. There were 8 of us, and we fell into a habit of going to lunch together every Friday. The check plus tip was always split 8 ways (or 6 or however many people came). One young woman (relatively new hire) had a habit of getting up to go to the rest room as soon as the check came. She would watch for just the right time when several people were engaged in lively conversation and laughing, etc. I noticed it, as did a co-worker. (She/cheapskate was not a kid - about 28 yrs old) The boss would just go ahead and collect from everyone then toss in some extra.
Errant co-worker would stay in the rest room until we were ready to leave, and I never saw her give money to anyone. It was hard to decide what, if anything, to do. So, after several weeks of this, a co-worker said to boss “I’ll pay X’s share and she can pay me back when she comes out of the rest room.” Well, when X came out of the rest room, co-worker said “They already collected and paid. Since you weren’t here, I paid your share.” X looked at coworker like she had two heads and did nothing. Next day, co-worker asked X for the money and X said “Oh, I have to go to the bank”. She gave several excuses over several days and actually started treating co-worker rather cool and avoiding her. I don’t know if X ever paid up, but I continued to notice that X did her disappearing act when it was time to pay. So, two of us started asking for separate checks and just paid for our own lunches. If boss wanted to pay for X’s lunches, fine, but I didn’t want to.